Remove CMS_TEMPLATES shorthand ...

...so it won't end up referencing to a different object when
tests asign to settings.__class__.CMS_TEMPLATES a different object.

Warning:
- a test in lunchbox/tests_admin.py that took advantage of the
  previous behaviour will fail unless LUN-1661 is integrated.

The problem
- The inital implementaion assumed settings.__class__.CMS_TEMPLATES
  would be initialized only once.
- DBTemplatesMiddleware uses the CMS_TEMPLATES shorthand for
  settings.__class__.CMS_TEMPLATES.
- When a test modifies settings.__class__.CMS_TEMPLATES, the
  CMS_TEMPLATES is NOT updated, it will reference the old object.
- When another test creates Template.objects.all() = [ stuff ], calls
  self.client.get('/admin/') it expects the middleware to put those
  templates in settings.__class__.CMS_TEMPLATES.value
- What actually happens is that the templates end up only in the
  CMS_TEMPLATES shorthand.