Dialog - changed the default behaviour for cancel (issue #48)

The default behaviour is not for escape to cancel a dialog (see supporting documentation for this in issue #48).
Added a new property to dialog to allow for escape to be disabled, so the old functionality can be enabled if required.

src/Dialog/Dialog.js

@@ -177,6 +177,7 @@ class DialogInline extends Component {
     open: PropTypes.bool.isRequired,
     overlayClassName: PropTypes.string,
     overlayStyle: PropTypes.object,
+    overrideModalEscKey: PropTypes.bool,
     paperClassName: PropTypes.string,
     paperProps: PropTypes.object,
     repositionOnUpdate: PropTypes.bool,
@@ -272,7 +273,7 @@ class DialogInline extends Component {
   }
 
   requestClose(buttonClicked) {
-    if (!buttonClicked && this.props.modal) {
+    if (!buttonClicked && (this.props.modal && this.props.overrideModalEscKey)) {
       return;
     }
 
@@ -516,6 +517,10 @@ class Dialog extends Component {
      * Overrides the inline-styles of the `Overlay` component that is rendered behind the `Dialog`.
      */
     overlayStyle: PropTypes.object,
+    /**
+    * Overrides the use of the escape key for cancelling a modal dialog
+    */
+    overrideModalEscKey: PropTypes.bool,
     /**
      * The CSS class name of the `Paper` element.
      */
@@ -554,6 +559,7 @@ class Dialog extends Component {
     autoDetectWindowHeight: true,
     autoScrollBodyContent: false,
     modal: false,
+    overrideModalEscKey: false,
     repositionOnUpdate: true,
   };