Empty field names are passed to the mergeDisplayFieldsForInstance function
Merge remote-tracking branch 'remotes/cpinter-commontk/276-dicom-database-display-tables' into 276-dicom-database-display-tables

Conflicts:
	Libs/DICOM/Core/ctkDICOMDisplayedFieldGeneratorAbstractRule.h
	Libs/DICOM/Core/ctkDICOMDisplayedFieldGeneratorDefaultRule.h
	Libs/DICOM/Core/ctkDICOMDisplayedFieldGeneratorRadiotherapySeriesDescriptionRule.h