Add set image UIButton extension methods
Merge branch 'master' into feature/button_image
Add button image format
Merge branch 'master' into feature/button_image
Add set image tests
Arrange cancel image tests properly
Define a UIView extension for UIKitGlobals and add a backgroundImageFetcherKey
Move hnk_formatWithSize to UIView extension
Refactor after pr reviews
Merge pull request #102 from Haneke/feature/button_image

Feature/button image, closes #79 #81