Fix opengever task tests.
Fixed OrgUnit Builder: allways create groups when assign users.
TaskBuilder: Add default values for required fields.

The SQL representation in `opengever.globalindex` defines no db-constraints
for the required fields, so it makes sense to define default values for
those fields.
Response and DocumentsTransporter: change behavior from remote-client
to remote-admin_unit.
Changed oguid composition: use admin_unit_id instead of the client_id.
Task overview: use admin_unit_id instead of the client_id.

Because of the task rework the ogduid and mandanten behavior has changed.
It's now the admin_unit who decide if a task is remote or not.
Fixed task css helper.
Diverse tests fixes: because of the task rebuild.
Change behavior of remote task requests and views.

Because the task model has changed,
it compares now the current_admin_unit's instead of the client ids.
pyflakes.