Fixed referenceprefix starting point for dossiers.

The referenceprefix startingpoint for dossiers should not be affected by the configured value in the registry (`IReferenceNumberSettings.reference_prefix_starting_point`). The dossier referenceprefix should always start by 1.
Merge pull request #150 from 4teamwork/pg_refernceprefix_starting_point_for_dossiers

Fixed referenceprefix starting point for dossiers.