#114 created RelationshipRenderer

The class RelationshipRenderer was created and it extends
RelationshipEditor. The editor has now a second constructor, with which
it can be made non editable. Furthermore the needed methods to also make
its subpanels non editable were created, but not implemented.
 #114 makeNonEditable() for AdditionalTagsPanel
 #114 makeNonEditable() for BasicPropertiesPanel
 #114 makeNonEditable() for SourceResourceRelationshipPanel
 #114 makeNonEditable() for TargetResourceRelationshipPanel
 #114 makeNonEditable() for MetaDataPanel

Made the three buttons to edit the metadatas invisible. Added a button
to open the MetaDataRenderer for the selected metadata. This is opened
in a dialog as the MetaDataEditor, therefore the MetadataRenderer now
implements EditorShowableInDialog.
 #114 changed the intents of the new button
Merge branch 'feature/114-relationship-renderer' into dev