Have activate user return json

- Change activate user from admin controller to return json
- Test that it returns json
- Remove unnessary test from log_out spec

This commit was created so that when you activate a user through the api
it returns a json response.
FIX: Fix rerendering issues on some components.
Merge pull request #3032 from awesomerobot/master

adding max-height for embedded video
The `{{i18n}}` helper should use quotes when looking up keys, always.
Merge pull request #3031 from oblakeerickson/activate_return_json

Have activate user return json
allow users to override groups if needed
correct random ')') showing up
FIX: In Firefox :w autocomplete was broken

Always use hasOwnProperty as opposed to [] on hash objects,
{} has a "watch" function in Firefox
clean html
FIX: add CDN support to emoji preview and toolbar
FIX: cache all public resources registered by plugins.

Plugins are responsible for expiry
prep work for emoji versioning
Add pagination for emoji, split out foods, make it wider
UX: Make category link text black in digest emails
Automatically include all `.hbs` files from plugins
Allows us to easily define routes in plugins
Move `register_asset` into `PluginRegistry` -- the logic works better
there.
When using automatic file includes (es6, hbs) from plugins, allow the
asset pipeline to find new and deleted files with deleting the `tmp`
folder and restarting the server.
add embedding notes to admin quick start
add embedding notes to install doc