Fixing error 500 on /groups and /teams.

Although these urls do not exist they were being mapped with rails
resources. I've added an exception not to add the index routes. Now they
will yield 404 errors instead of 500 ones when trying to access /groups
or /teams.
Merge pull request #3740 from vialink/5-1-stable

Fixing error 500 on /groups and /teams.