Avatars and Membergroups

[Senkusha]

A few minor updates:

* Added avatars to the topic index to better identify who started and last posted to a topic.
* Added avatars to the Member list.
* Color coded the Membergroups.
* Added a filter for each Membergroup, so that if you choose a Primary Membergroup other than Registered Members, only the Boards of your interest will show up.
* Added a description for each Membergroup.