Many minor edits to Master while checking on recent merges

Here is a list of most notable edits:
* SamplingFeatures: added FK from Sites.LatLonDatumID to
SpatialReferences.SpatialReferenceID
* SamplingFeatures: Changed SpatialReferences.Notes to SRSNotes
Flipped diagrams for ExternalIdentifiers, Annotations and Extensions,
so that the parent tables from ODM2Core schema are above, indicating
that they are the base class to their respective cross-reference
tables/entities.
Various table/field comments and diagram notes are edited throughout.