Merge branch 'release-0.4.7' into develop
Changed default datetime for audit fields to use timezone.now()

The previous default value was datetime.datetime.min however this was
triggering an overflow error when creating the SQLite database for the
demo site.
Requirements allow argparse to be loaded from an external repository.
Update Species to allow longer names.
Completely overhauled the way reference data is managed.

* Merged the reference data files for Activity, Age, Direction, Plumage,
  Protocol and Sex into a single file. The number of records will always be
  small so managing all the translations will not be difficult.

* (Species) Rank is now also handled by a single file however the data was
  replaced with the names used by eBird.

* Completely overhauled the way the reference data for Species and
  SpeciesGroups which makes it way easier to manage. A single file,
  taxonomy.csv, which is published by eBird is used to load all the Species
  and SpeciesGroup records. From this a subset of records can be selected
  and translations for common names loaded using species checklists published
  by Avibase. Then all the records for species that occur outside a given
  geographical area can be removed making the process of managing the species
  table much easier.
Updated version number for release
Merge branch 'release-0.4.8'