Added Citations to Methods & Annotations

Used two different approaches, as discussed in #45:
* Bridge table to Methods in Provenance schema, similar to
DataSetCitations.  This enables compound methods and also keeps a
foreign key to optional tables out of the Core.
* Direct foreign key to Annotations, as its not as likely that an
Annotation will need more than one Citations, and Annotations are also
optional.
Reordered RelationshipTypeCV in list to be between Subject & Object FKs

As discussed in issue #45.  Also:
* Added FK to RelatedCitationID field.
* Changed field name: ParentFeatureID to RelatedFeatureID
Added ParentAnnotationID

to allow for simple Annotation of an Annotation (recursion), as
described in issue #41.
Modifications to annotations

1.  Removed ParentAnnotationID and its recursive relationship from
Annotations.
2.  Created RelatedAnnotations entity.
3.  Added AnnotationLink to Annotations.
Modified Provenance diagram to show RelatedAnnotations
Merge pull request #50 from UCHIC/Annotation-Method-Citations

Merge Annotations-Methods-Citations branch into Master