Merge pull request #926 from caridy/frame-addon

moving part of the logic from HTMLFrame into assets addon to facilitate customization of the frame:

- Add support for inheritance over HTMLFrameMojit or just create a brand new frame that uses a set of addons to create a frame. In this gist I demonstrated both approaches: https://gist.github.com/4543247
Merge branch 'develop' of github.com:yahoo/mojito into frame-addon