moving part of the logic from HTMLFrame to mojito-frame-addon

The idea here is to make the creation of Frames Mojits a breeze.

Based on the current implementation we can create a mojit that inherit from HTMLFrameMojit or just create a brand new that uses a set of addons to create a frame. In this gist I demonstrated both approaches:

* https://gist.github.com/4543247

Todo:

* Document re-usability of the HTMLFrameMojit methods (this is for Joe)