NXP-12286 add update/create/delete support on groups
NXP-12286 Enforce and refactor guard
NXP12286 enable add/remove of user to/from a group
NXP12286 fix bad test
NXP-12286 refactoring : extract common patterns in abstract objects
NXP-12286 Add test to verify power users guards
NXP-12286 Enforce unicity of test and better isAPowerUserEditableGroup scheme
NXP-12286 Remove local check and use common one
Merge branch 'master' of github.com:nuxeo/nuxeo-features