Remove sites framework

[bufke]

Remove Django sites framework, which duplicates functionality of existing django settings.

Resolves TASK-424

Notes

• Review user_auth.py change

For reference, the default is:

In [6]: site.name
Out[6]: 'example.com'
In [7]: site.domain
Out[7]: 'example.com'
In [10]: settings.KOBOCAT_PUBLIC_HOSTNAME
Out[10]: 'kc.kobotoolbox.org'

[noliveleger]

It does not pass locally (because my domain name is not kc.kobotoolbox.org)
I guess we could use something like:

from django.test import override_settings

class CustomContextProcessorsTest(TestCase):
    @override_settings(KOBOCAT_PUBLIC_SUBDOMAIN='kc.domain.tld')
    def test_site_name(self):
         context = site_name(None)
         self.assertEqual(context, {'SITE_NAME': 'kc.domain.tld'})

[bufke]

I tested by setting KOBOCAT_PUBLIC_SUBDOMAIN to another value. Test failed. With recent commit, it now passes. The specific override needs to be "KOBOCAT_PUBLIC_HOSTNAME"