Edit community profile

The following PR depends on #27, #29 and #30.

It implements the functionality of editing community profile. 
I think we should not check against groups... A group is a collection of permissions, so by saying this user should be from Community Admin group, you also ask from the user to have all other permissions that are not required to edit the community profile.

I see Groups as a convenient way to assign permission to users - admins wouldn't like to manually assign each permission to each user. By checking for a specific permission, we are asking the minimum from a user. Also some users might have a very specific set of permissions (like Backup Admins - for which we don't have a Group, but it might be created easily from the admin panel).

I would probably remove this `@admin_required` check. What do you think?