Added support for UIImage's initWithData:scale: methods that were added in iOS6
Consolidated the frame retrieving code in the process.
Grouped instance & class methods.
Removed the extra check to make sure UIImage supports the iOS6+ initWithData:scale:
Only create displayLink if there is an animated image.

Also fixes a crash where `changeKeyframe:` would be called without an animated image.
DRY code
less hardcorded class names.
Merge branch 'DRY-OLImage'