Add ability to increase text size in the commit details tab

[rtyley]

Nikolay asked for the ability to increase text size in the commit details tab - pinch-zoom would probably be the nicest way to do this. For a WebView that would probably implemented by default, but not so with a TextView - probably need to use android.view.ScaleGestureDetector:

http://android-er.blogspot.co.uk/2011/11/detect-pinch-zoom-using.html