Simple port of Class2Go's chat feature

Embed a chat widget (much like the calculator widget) into the
courseware. To use, you must point it at an ejabberd box,
configured as `JABBER_DOMAIN` in the settings.
styled simple-chat to look better!

- styled the send button
- styled the room tabs
- added jquery scripting to connect on tab click
Removed X on groupchat and styled chat tabs

- The X close button has been removed from the groupchat tab
- chat tabs have been styled to be able to scroll sideways

(still need to add left and right arrows but chat is very usable as is)