add set_default_permissions and set_permissions to PermissionLevelImixin
use group.slug in ajax_lookup
Move to using set_default_permissions and set_permissions from PermissionLevelMixin in Layers, Maps, Documents
Merge branch 'groups-redux' of https://github.com/garnertb/geonode into groups-redux
Move permissions views to geonode/security/views.py
Fix imports
Fix security tests to use new setup
Add signal to automatically set group permissions when groups are added to an object.