Test Taxonomic Classifier implementation

Added TaxonomicClassifiers table to ODM2Core schema, and also a
TaxonomicClassifiersExternalIdentifiers cross-reference table in the
ODM2ExternalIdentifiers schema (whew! long table and field names!).
TaxonomicClassifiers could be shortened to Taxa or Classifiers (IEDA
uses Classification), but I think that these do not convey the full
range of uses quite as well.
TaxonomicClassifiers Diagram
ExternalIdentifiers diagram, with TaxonomicClassifiers cross-ref.
Taxonomic Classifier edits during call

Edits during call included:
* Changed “Taxon” to “TaxonomicClassifier” in all field names and
comments.
Pull upstream from Master & SamplingFeatures_em branches

I did a line by line code compare, and once SamplingFeatures_em gets
merged with the Master, then this branch (TaxonomicClassifiers) should
be favored during any merge conflict.
Cosmetic changes to DBwrench diagrams.

This version includes all recent commits in the Master,
SamplingFeatures and TaxonomicClassifier branches.  It should become
the new Master.
Resolving conflicts in Taxonomic Classifiers feature branch
Removing figures from schemas folder

There were some figures in the schemas folder that showed the changes.
I don’t want these in the master branch, so I’m getting rid of them.
Merge pull request #15 from UCHIC/TaxonomicClassifiers_FeatureBranch

Merging Taxonomic Classifiers feature branch after resolving conflicts and removing extra images from the schemas folder.