finalize private chat and add new command

- added 'me' command
- private chat functionality complete
- message style modifications (style depends on message type and display
stored in database)
- private chat button no longer appears beside user's own username
- 'hidden' class is not added multiple times to helpMessage
- help message hidden after message sent (not command)
- improved command handling (regex and splitting)
- switched to unstable angular distribution for the ng-trim attribute
- fixed bug that occurs when new private chat opened up inside existing
private chat
- escaping username for generated private chat window URL