Rename GroupRole to Group

This removes Role and UserRole entirely.
Add permissions to User
Add indexes for lookup of User or Group by access to a resource
Merge branch 'user_permission'

* user_permission:
  Add indexes for lookup of User or Group by access to a resource
  Add permissions to User
  Rename GroupRole to Group
Fix processing of empty ObjectIds in Flask-Admin
Merge branch 'admin-objectid'

* admin-objectid:
  Fix processing of empty ObjectIds in Flask-Admin