Remove tastypie and all tastypie api stuff.
DRF + requirements
Setup api urls + users api view
+ regions & settings read-only no-filtering API
/api/files/
/api/pages/.

Because DRF brings in the model's fields' validation code, we need so
much less manual validation code than we needed with tastypie.
/api/maps/
/api/redirects/
Experimenting with page tags
tags in /api/pages/ + how to change
Historical API resources. Missing tags for now.
Versioned tags in api
CharField, not SlugField, for pg, redirect slugs

+ validate_page_slug to validate.

This is because the default SlugField validation, if invoked, will
over-ride the correct page slug validation.  We may want to just
create our own PageSlugField here.
Use GeoJSON geometry field on /api/maps/
GeoJSON in /api/regions
db_index=True on date_joined for User
Point to custom DRF-filter, rm custom DRF-gis
Working through apps, adding filtering support

Not complete yet.
/files/ api filtering
/pages_history/ filtering