Add an "info" View for the groups

A moderator in a Group has several menu items related to the configuration and membership of the group: Configure Group; Manage members; Invite new members.

But now that we've cleaned up our menus to be smart about permissions, a non-moderator member sees none of these.

We need some sort of non-moderator "info" view for the Group, where the user can find information on the Group, including:

• High-level summary info about the Group
  • Name
  • Avatar image
  • Topic
  • Creator and creation date (???)
• The Matrix room ID (maybe hidden behind some "advanced" config)
• The list of admins and moderators for the Group
• The list of members in the Group
• A button to leave the group