Typo fix.
[Fix bug 773647] Add categories in events

* Change Event model
* Change EventForm form
* Implement UI on edit and view event
* Expose categories in events api
* Implement filter by event
* Changes in unittests to include categories
v1 of proper update.py script for remo chief, see https://bugzilla.mozilla.org/show_bug.cgi?id=827423
v1 of proper update.py script for remo chief, see https://bugzilla.mozilla.org/show_bug.cgi?id=827423
Merge pull request #365 from johngian/773647

[Fix bug 773647] Initial implementation of categories in events