MMDrawerBarButtonItem improvements

- touch/highlight-state support in iOS7
- added initWithCoder: for xib/storyboard support
- touch-action sender is now the bar button item itself vs a UIButton
oops fix - correct action/target for iOS6 code path
Fix for issue #123: MMDrawerOpenCenterInteractionModeNavigationBarOnly fails if navigation controller's toolbar is shown.
Merge remote-tracking branch 'tomswift/master' into 119
Clean up
Merge pull request #124 from tbveralrud/master

Fix for issue #123