General housekeeping

Removed useless comments from controller and made a note in services
that sharing the controller among 2 directives is calling the controller
twice. Since the initialisation code is not wrapped in a function that
will run only once, it is called twice, making the code call the backend
API twice as many times as necessary.
Fix bug with question creation

Creating a new question was updating the title, but not the entire
editor contents. This is now fixed to update the editor with the
contents of the newly created question.
Limit question types accepted via front-end and back-end

Front-end options supplied via question creation form limited to
true/false and multiple choice questions. Back-end validation also
limited to these two choices.
Fix bug with question editing
Implement different answer sub-section and saving via a service

A massive commit of rushed code to push out the necessary features.
Calling NavCtrl twice is now having a knock-on effect on performance by
making unnecessary HTTP requests. Controllers are in need of a good
refactor and cleanup.