Add a SimpleScanViewController for full UI customization

[kingst]

This PR is for our programmatic UI extension to ScanBaseViewController. We'll use this to show how people can fully customize our UI. This new class is meant to be complete but bare bones from a UI perspective. People can use it directly if they like the look and feel, or the can modify variables or subclass for more control.

In a future PR we'll:

• Add examples to show simple UI customizations.
• Migrate our fraud ViewControllers over to use this.
• Migrate ScanViewController over to use this as a base class.

[jaimejiyepark]

looks good. one thing though: is it a good idea to have another scan delegate protocol for simple that looks exactly like the original? or should we make the scanVC protocol more generic to accommodate simple

[kingst]

It's a good question and my first cut did this but I created a separate protocol for two reasons (1) I don't want to change public interfaces unless we get a massive simplification, which isn't there case here and (2) we're going to use this as the base for fraud challenges which don't need skip, so the interface isn't a good match

[jaimejiyepark]

hmm alright then. something to keep in mind. #shipit