Fixed and improved user auth. Init of XF addon.

What is working :
- Registered Users auto login/logout (on XF logout).
- Guests (if enabled in options)
- Forums as channels, based on XF permissions
- AJAX-Chat options can be overriden by those set in AdminCP (only "botchat
  name" option implemented yet)
- Code documentation

TODO :
- in-page integration + popup
- Channels alpha sort
- Redirect on logout (or else, registered users get logged back in)
- complete options list in AdminCP and in override function
- Styling ? At least XF template support.
Merge branch 'master' of https://github.com/ManOnDaMoon/AJAX-Chat