Adds git commit message in diff view.

This commit modifies the API slightly to allow retrieving the git commit
message from a commit, and displays it in DiffActivity. A new View is
created, MessageView, responsible for displaying the text from the
commit message, similar to DiffView. No formatting is done to the text
yet.
Removes debugging left in CallBack.

This removes code I left in to print out in LogCat if the application
failed to retrieve the commit data from the server. This does not use
Crouton to show an error message if it failed to connect, because the
diff CallBack already does this, and if it failed to connect to the
server, it would display two error messages.
Adds menu option to disable text wrap

This feature adds a checkable menu option to toggle wrapping lines of
code and commit messages to the width of the screen in DiffActivity.

This was achieved by creating a custom HorizontalScrollView with an
onMeasure method that measures its child with an exact MeasureSpec of
its own width. If wrapping is disabled, the super method is called,
making it act just like a normal HorizontalScrollView.
Merge pull request #17 from JosephTurner/feature/commit-msg

Feature/commit msg