Adds iOS 7 Support

Support for iOS 7 UIAlertView, this uses a container instead of removing layers
Merge branch 'iOS7' of https://github.com/aparedes/GIDAAlertView into aparedes-iOS7

Conflicts:
	Demo/Demo/GIDAAlertView.h
	Demo/Demo/GIDAAlertView.m
	GIDAAlertView.h
	GIDAAlertView.m