Merge 'projects' and 'groups' tab in the admin interface

Description

Currently, when viewing a user account in the admin interface, there is a 'groups' tab which displays the groups tab a user is a member of (and allows you to remove them from that group) and a 'projects' tab which also displays the groups that the user is a member of.

Proposal

The 'groups' tab seems redundant, as the 'projects' tab could be made to replicate the same functionality. It shouldn't, IMHO, require too much work to merge the two tabs.