update python3 status of dependencies
script for importing ddr-densho entities from CSV
mod script to add importing of ddr-densho files from CSV
improve file import script's user feedback
slightly better import script walkthroughs; formatted in rst
CSV header validation; better CLI feedback; code cleanup
Updated descriptors in genre choices list in entity.py
replace variant header names, controlled values with official terms

Somewhere along the line bad header names and values for
controlled-vocab fields have crept in to the spreadsheets.

This change adds dicts of variant terms that are used to build
indexes.  These indexes are used to replace variant terms with
the official ones.  The user can add to the variant term dicts
as they come across them.
functions for loading entities and testing files before import

These attempt to load Entities and test for file presence and
readability before starting an import.  Hopefully this prevents
long imports getting interrupted and having to be restarted.
added optional "digitize_person" and "tech_notes" fields to File
Merge branch 'master' into 099-inventory