Release 3.1.0

  - remove unused UserController
  - add signal handler for SIGTERM
  - update V3_0_02__file_population migration to apply leading slashses
    to ace tokens so later migrations are able to be applied properly
  - corrected the cte used for updating the fixity table by querying on
    the tagmanifest to assign the correct file_id

  - allow nullable field (note) on StorageRegion

  - specify fields on Depositor can be null

  - hash smtp reports in order to prevent spamming of reports
  - remove unused smtp properties
  - make sure we call exit after handling SIGTERM