Stuff for ios6
Small updates
Added new tableGroupedBackgroundView prop, fixed mask for grouped label.
TextLabel takes maximum amount of space if no detailText is set.

This fixes a bug where button labels text did not get properly
centered (because the frame didn't span the entire cell).
Merge pull request #546 from bartvandendriessche/fix/button_text_alignment

TextLabel takes maximum amount of space if no detailText is set.
Added iconNamed method for iOS7
Fixes bugs related to iOS7
iOS 6 doesn't have this feature.
Merge remote-tracking branch 'upstream/master'