Added last_update datetime column to db.
Updated test data and csv->db mappings.
Updated Item Model to use new last_update column.
Merge branch 'master' into CCH-1110
Merge branch 'master' into CCH-1110
Adding HEAD request to the Item REST API.
renaming column
Merge pull request #786 from cschroed-usgs/CCH-1110

Cch 1110