Fixed backend issue with group building.

If a user ever became a member of the group, when they leave, the search results will still indicate that they are a member. A similar issue could occur with the admin flag, which would cause a 403 error since the user was allowed to access the manage page, even though they weren't truly an admin.

When a group is build in GroupService.java, the user could only ever be set to be a member of the group, and the flag would never be changed, even when the user was no longer a member. It now handles when they aren't members or admins.