Recently functions were added to zaza.model for adding and removing
models. These duplicated existing functions in zaza.controller.
Given these functions act against the controller, zaza.controller
feels like the correct location. In addition the implementations in
zaza.controller correctly handle disconnects which the new ones
did not.
This PR removes the duplicates and points any existing references
from zaza.model to zaza.controller. Finally, docstrings were added
and documentation links.
