Adjust the test setup and helpers that all the tests can handle with the OrgUnitSelector.

Some tests had need some ajustments in the setup as well.
Fixed markup in ou_selector_viewlet.
Temporarily disable some tests, which has to be reworked and reviewed
after implementing the OrgUnitSelector stuff.
Dropped senseless tests.

When testing this feature the test should be written new completly.
Use `assigned_users` on a OrgUnit instead of `IContactInformation.list_assigned_users`.
Added `current_admin_unit` getter.

Including corresponding registry entry (Upgradestep is missing).
TMP added upgradestep to creating additional AdminUnit table.
TMP: Dropped no longer used contact info method `list_assigned_users`.
Added dependency to alembic.