Bugfix: Renamed static final int in DOIIdentifierException.

Renamed DOIIdentifierException.REGISTER_FIRST to
DOIIdentifierException.RESERVE_FIRST.
Bugfix for DOI support using DataCite.

The DOIIdentifierProvider checked whether a DOI is reserved or
registered at the registration agency already. This should be done by
the DOIConnector if it is necessary at all.
Bugfix: DataCiteConnector ignored the configured scheme.
Bugfix: Changed modifiers in DataCiteConnector.

Set the modifier of some variables and methods from private to
protected. This makes it easier to extend the DataCiteConnector.
Changed DIM2DataCite.xsl to not discover provenance information.

dc.descritption.provenance contains personal information. Removed it
from DIM2DataCite.xsl to not discover it.
Merge pull request #404 from tuub/DS-1804

DS-1804