Custom functions in settings for name, picture and relationship

The only thing that I didn't like about this module is that by default it looks at the user name and picture with no means to change that.

Inspired by deven_ I made some additions and attached the patch. The changes consist of adding 3 fields to the configuration settings that can be used to enter a custom (other module or your own) function for getting the name, picture and relationship for a user. The relationship determines which users are displayed in the buddy list and which messages you get to see in the public chat room. The admin form validation checks if the functions entered exist.

I'm not creating patches too often and I couldn't find the GIT repository for the beta's so I created one manually. You probably need to enter the file names to patch yourself when you apply it. I created the patch for beta 28, but a quick check showed it should work on beta 29 as well. Would be great if this patch could be accepted and included.

Finally a big thanks to the creators and maintainers of this module. It is truly awesome that advanced modules like this are shared. I hope I can contribute with this patch.