bugfix: `es_update movies --newer --workers`

• fixes #31 es_update movies --newer --workers does not store worker information

Fix es_update --newer and fix es_update use of pks

• fix bug #21 wrong batch update total using multiprocessing in 0.7.1
• fix bug #23 KeyError _index_version_name in es_update --newer
• fix bug #25 use pks for queryset inside workers
• add enhancement #26 add timestamps to log messages

Add --es-only to es_create and es_dangerous_reset

• fixed gh #8 es_dangerous_reset --es-only to sync database to ES
• fixed gh #17 make es_dangerous_reset remove dem models
• improved test coverage
• added tests for es_create --es-only
• added IndexVersion.hard_delete() (not called by default)
• added hard_delete flag to DropIndexAction
• added hard_delete flag to DEMIndexManager.test_post_teardown()
• updated __str__() of IndexAction to be more descriptive
• made using an index not authored in current codebase more forgiving, logging a warning

Add Python 3 Support and Tests

• fixed gh #5: "add python 3 support and tests"