Major refactor

The major thing added here is that metadata is correctly handled in
most (all?) cases. I also think some bugs have been fixed, but I did
not check the bug list ;)

As a foreword, I want to say that I am far from being an expert in
either Objective-C nor the iOS APIs (I only did some basic patches
before). So please correct me if I say/did anything wrong.

As a general design decision, I tried to break all the workflow in
small readable methods that either return something (I chose to use
reference passing when returning more than one result which I find
clearer than returning an NSDictionary where the result is specified
nowhere), or use the convention completionBlock / resultBlock /
failureBlock which it seems Apple APIs use.

There are three main paths from the image retrieval to the result.

1. The user wants the original image from the PhotoLibrary or from the
SavedPhotoAlbum with a destination type NATIVE_URI.
2. The user wants a modified version of the image, wherever it comes
from.
3. The user wants the geolocation.

There are also some combinations of options that are disallowed because
they don’t make any sense:
1. if the user wants an image with a source type CAMERA, and a
destination type NATIVE_URI, he has to save it to the photo album. An
image that is not there does not have a NATIVE_URI.
2. if the user wants an image with a source type PHOTOLIBRARY or
SAVEDPHOTOALBUM, needs editing (resize, orientation correction), and a
destination type NATIVE_URI, he has to save it to the photo album.
Otherwise, we would return the original image with no modification.

As we can see, if we want a destination type of NATIVE_URI, there are
only two possible paths: either we want an unmodified version of a
library image, or we need to save to the photo album.

Regarding metadata, we do not need it in only one case, when the
destination type is NATIVE_URI, the source is the library, and no edits
have to be done.

Otherwise, we need to either fetch if from the
UIImagePickerControllerMediaMetadata key of the info dictionary
provided by UIImagePickerController in case the source type is CAMERA,
or from the ALAsset corresponding to the library image (see
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UI
ImagePickerControllerDelegate_Protocol/index.html#//apple_ref/doc/consta
nt_group/Editing_Information_Keys).
This actually introduces asynchronicity in the metadata retrieval,
since we first need to fetch the ALAsset using
UIImagePickerControllerReferenceURL. *We cannot use UIImage as it
strips out most (all?) of the metadata*.

Once we actually retrieved the metadata we need to modify it for every
transformation of the image (orientation, resize, gps).

In the previous code, the saving was done after computing the
CDVResult. This is not the case anymore as we need access to the saved
ALAsset when we want to return a NATIVE_URI. The saving is now done
after all image editing has occurred.

Since the metadata retrieval and the album saving is done
asynchronously, the process pipeline itself is made asynchronous. We
can use resultBlock and failureBlock to get the processed image with
its corresponding metadata or to get the image Asset NATIVE_URI.

CropToSize is not a valid option (it is always set to NO anyway) so it
has been removed.

The documentation lacks some clarity for two things (see FIXME apache#1 & apache#2):
-  Does the quality option apply to the library images as well. This
would mean that we cannot use NATIVE_URI with the quality set, except
if we save to the photo album.
- Does the orientation correction apply to the library images as well.
Same thing. I actually removed that options at first, but this would
mean that we need to read the EXIF data in the js code and orient the
image appropriately (except for NATIVE_URIs since the web view does
that automagically, but orientation correction does not make sense
here).

- usesGeolocation does not make sense for an image with a source type
other that CAMERA (maybe on some fringe cases?)
- fix a bug where allowsEdit + saveToPhotoAlbum + NATIVE_URI make the
image save in the wrong orientation (despite the metadata having the
correct orientation afaict)

WARNING:
I did not test the usesGeolocation option due to a lack of time (and,
frankly, a lack of interest;).

ACKNOWLEDGMENT:
Shoutout to @athibaud who also took part in the refactoring effort. Any
bug’s on him! ;)

src/ios/CDVCamera.h

@@ -80,26 +80,62 @@ typedef NSUInteger CDVMediaType;
 
 // ======================================================================= //
 
+typedef void(^CDVCameraReadMetadataCompletionBlock)(UIImage*, NSDictionary*, CDVPictureOptions*);
+typedef void(^CDVCameraProcessImageResultBlock)(UIImage*, NSDictionary*, NSURL*);
+typedef void(^CDVCameraProcessImageFailureBlock)(NSString*);
+
 @interface CDVCamera : CDVPlugin <UIImagePickerControllerDelegate,
                        UINavigationControllerDelegate,
                        UIPopoverControllerDelegate,
                        CLLocationManagerDelegate>
 {}
 
 @property (strong) CDVCameraPicker* pickerController;
-@property (strong) NSMutableDictionary *metadata;
+@property (strong) NSDictionary* metadata;
 @property (strong, nonatomic) CLLocationManager *locationManager;
-@property (strong) NSData* data;
+@property (strong) UIImage* image;
 
 /*
- * getPicture
+ * takePicture
  *
  * arguments:
- *	1: this is the javascript function that will be called with the results, the first parameter passed to the
- *		javascript function is the picture as a Base64 encoded string
- *  2: this is the javascript function to be called if there was an error
+ *  1: success callback (called with either Base64, file URI or native URI)
+ *  2: error callback
  * options:
- *	quality: integer between 1 and 100
+ *  - quality (number [0-100])
+ *  - destinationType (number):
+ *    0: DATA_URL => Returns a Base64 image
+ *    1: FILE_URI => Returns a file URI
+ *    2: NATIVE_URI => Returns a native URI (asset-library://...)
+ *  - sourceType (number):
+ *    0: PHOTOLIBRARY
+ *    1: CAMERA
+ *    2: SAVEDPHOTOALBUM
+ *  - allowEdit (bool)
+ *  - encodingType (number):
+ *    0: JPEG
+ *    1: PNG
+ *  - targetWidth/targetHeight (number)
+ *  - mediaType (number):
+ *    0: PICTURE
+ *    1: VIDEO
+ *    2: ALLMEDIA
+ *  - correctOrientation (bool)
+ *  - saveToPhotoAlbum (bool)
+ *  - cameraDirection (number)
+ *    0: BACK
+ *    1: FRONT
+ *  - popoverOptions (dictionnary) [iPad only]:
+ *    - x (number)
+ *    - y (number)
+ *    - width (number)
+ *    - height (number)
+ *    - arrowDir (number):
+ *      1: ARROW_UP
+ *      2: ARROW_DOWN
+ *      4: ARROW_LEFT
+ *      8: ARROW_RIGHT
+ *      15: ARROW_ANY
  */
 - (void)takePicture:(CDVInvokedUrlCommand*)command;
 - (void)cleanup:(CDVInvokedUrlCommand*)command;