* extends user and group structure by introducing fields for issued and integration references
* Add integration checks to group management to prevent groups added by integration.
* Add integration checks to user management to prevent deleting user added by integration.
* Fix broken user update tests
* Initialize all user fields for testing
* Change a serializer option to embedded for IntegrationReference in user and group models
* Add issued field to user api response
* Add IntegrationReference to Group in update groups handler
* Set the default issued field for users in file store