Merge pull request #54 from benvium/master

Fix for #52: Fix non-retina appearance of border created in +[NUIGraphics backButtonWithClass:]
Cleaned up NUIFileMonitor, removed unnecessary source types
Using setBackgroundImage for Button:background-color

setBackgroundColor is overwritten is some cases (e.g. UISearchBar's cancel button)
Added renderText:withClass to NUILabelRenderer to bypass application of Button's background-color to Label

UIButton titleLabels should have a clear background color, so that their color isn't at odds with the button color during other control states
Only applying UITextField padding when necessary; not styling UITextFields within UISearchBar