Fixed #51: Track bug assignments

Add a control to the demo page to assign a new or open bug to a
demo-cat user.  Introduces a new ML REST endpoint to return the list of
users.  Uses a customized version of the allmighty-autocomplete Angular
directive.
Reset bug form when user clicks cancel

The cancel link now properly resets values for a bug when a user hits
cancel.
Fixed #66: Revert value when user clicks cancel

The Editable directive now resets the model’s value back to the
original when a user clicks cancel.  Added two new functions:
getOriginal() and cancel().
Use the username for bug assignments, as opposed to the user’s full
name.  Addresses comment in pull request #67.
Merge pull request #67 from mariannemyers/master

Fixed #51 & #66: Track bug assignments and make cancel work as expected