Support organizations in web service api/user_groups/update

The web service api/user_groups/update must provide the optional parameter organization. It references the organization of which the group belongs to.
When parameter is not set, the default organization is used to find the group by its name.

The permission to administrate the organization is required.

The feature "default group" (automatic membership of new users) relies on the property sonar.defaultGroup. As organization settings are not implemented yet, this feature "default group" must be disabled on non-default organizations. The property sonar.defaultGroup must not be updated when dealing with a non-default organization.