Remove link to admin interface
Inherit OTIUser from AbstractUser

Extend from AbstractUser, rather than AbstractBaseUser

We get all the default functionality of the
django.contrib.auth.models.User class without having to reimplement
anything. This makes it easy to add additional custom fields/methods
in the future.

NOTE: This commit requires a 'DROP DATABASE transit_indicators;'
and then a re-run of the provision script
Add permissions for API views

There are two new viewsets, which inherit from ModelViewSet
  - OTIAdminViewSet
  - OTIBaseViewSet

This allows the settings/configuration views to be read-only for regular
users, and editable by admin, which is defined as having
is_staff == True

Default permissions are full access for regular users,
must be authenticated
Merge pull request #60 from WorldBank-Transport/feature/auth-permissions

Feature/auth permissions