Don't remove histology work lists after registration

[Nicklas Nordborg]

This causes permission problems since users are normally not allowed to remove items. This has not been noticed before since the same user has been responsible for both creating the work list and registering the embedded paraffin blocks.

But the work lists can't remain in the work flow either so we must find a way to tell the difference between unregistered and registered work lists.

Unfortunately, biomaterial lists can't have annotations and there is no creation date property either. The only possible solution is to change the 'externalId' property to some other value that (eg. net.sf.basedb.reggie.histology.work-list.completed).

A workaround for the current situation is that the user that created the work list (or an administrator) manually give 'DELETE' permission to the user that is going to register the paraffin blocks.

[Nicklas Nordborg]

(In [2190]) Fixes #557: Don't remove histology work lists after registration