CONNT-25: Updating application and project to use Django 1.11.x:

- Bumped Django version in both the development requirements and setup
script to 1.11.x.
- Bumped Django Crispy Forms to version 1.7.0 in both development
requirements and setup script.
- Updated import of URL-related modules to use the new path (previous
one is deprecated).
- Added explicit on_delete = models.CASCADE option to all foreign key
fields (old implicit behaviour will be deprecated in Django 2.0).
- Fixed the custom change_list.html template used in Django Admin to
render without errors.

CONNT-25: Updating appliction and project to use Django 1.6.x:

- Fixed tests to denote that ordering is not important in a number of
queryset tests.
- Replaced deprecated parameter name mimetype with content_type in views.
- Updated development requirements and setup script to depend on Django 1.6.x.
- Removed requirement for django-discover-runner, which is now incorporated
into Django itself and works out of the box.
- Updated development requirements to include pytz (needed for USE_TZ = True
setting).

CONNT-31: Fix incorrect version requirement for Django Crispy Forms:

- Implemented test helper for verifying that no exceptions are thrown when
responses are being rendered.
- Updated all tests related to views that render responses to use the new
mixin.
- Updated development requiremnts to use correct version of package.
- Updated setup script ti require lower version of package.