Merge pull request #2 from dnajd/master

work from sunday pair
Added method to return map of joint changes: difference in value if changed, else None
Changed translator to be a class and added way to get hold of a translator without knowing the full class name
Changed UI to use core method to obtain translator
Added link to Kivy download. Closes gh-3
Added status field at bottom of UI. Use self.add_status() to add text to status window. Closes gh-7
command matching algo