Edit community profile

The following PR depends on #27, #29 and #30.

It implements the functionality of editing community profile. 
What if somebody is given the permission to change the community and is not an admin? Let's say the admin of the community trusts one particular person and gave him/her this one permission to update the community profile.

Well, according to the latest updates on permissions using django-guardian, it should be like this - `@permission_required_or_403('dashboard.change_community', (Community, 'slug__exact', 'community_slug'))`