Add convenient method to UIButton to set a background color as an image.
Add convenient method to UIButton to set a background color as an image.

vector-im/riot-ios,vector-im/riot-ios,vector-im/vector-ios,vector-im/riot-ios,vector-im/vector-ios,vector-im/riot-ios,vector-im/vector-ios,vector-im/riot-ios,vector-im/riot-ios