Add uniqueness constraint on GroupPagePermission, and error tags in template
PEP-8
Extend inline chooser panel templates to group create views
Update wagtailusers.tests to supply formset.management_form POST data
Require change_group_perm for access to groups views
Amend GroupForm.save(), so as not to blat non-user-facing django permissions
Add tests for group, permission and page-permission editing