Several minor changes - fixes and features.

- Added a custom filter to reverse an array.
- Added a gulpfile with a default task that starts a development web
server, serves the client application, watches for changes made to the
HTML, CSS or JS files and reloads the server.
- Removed ThreadManagerController, NotificationsController.
- Added API methods in ThreadService to manage open thread data,
generate title, create temporary threads etc.
- A thread is now opened when a user/group is clicked.
- CSS fixes. Also, threads float to the right.
- Limit number of open threads to 3.