MDL-40368 tool_capability: overall improvements made

* Can now compare multiple capabilities at the same time.
* Capability search now persists between requests.
* Upgraded to use renderers.
* Upgraded module.js to YUI shifted module.
* Converted deprecated calls.
* Converted forms to Moodleforms.
* Implemented backend functionality to overview at
  different context levels. Not possible presently as
  there are no front end hooks.