Update help bar, remove obsolete stuff.

Some of these commands are impossible to implement in XMPP,
or would require significant server extensions.
Support /me command (XEP-0245).

XEP-0245 describes a special command that receiving
clients can represent as an action ("/* User <text>/").
The command should be transmitted unaltered, and only
affects client representation.

This required some rewriting of ui.messageCreate.
Also, ui.formatUser is now visual.formatUser.
Bugfix in messageInsert; s/return/break/.