Update keyboard-related api urls to /api/keyboards/
Updated cc_kapi views for correct RESTful behaviour

* Added simple DefaultKeyboardView to handle default keyboards, in its own
endpoints
* Added KeyboardsListCreateView to provide a ListView when visiting
/keyboards/ which will make for easy front-end development of
user-keyboard-switching
* Renamed KeyboardView to KeyboardGetUpdateDestroyView to better describe
function. This now handles the whole keyboard-detail handling.
* KeyboardGetUpdateDestroyView no longer tolerates anonymous users, returning
correct 403, rather than a DEFAULT_KEYBOARD instance.
Rename KeyboardsView to KeyboardGetUpdateDestroyView
Update tests for new API behaviour
Updated URLs to use new view endpoints
Correct front-end to use new endpoints
Remove unnecessary import
Simplify get_object behaviour in KeyboardGetUpdateDestroyView
Merge pull request #240 from jvc26/cc_kapi-default-behaviour

Cc kapi default behaviour