Remove django-settings-context-processor and define better ways to handl the values it passes

Too trivial to have a dependency for it. Also, seems like an anti-pattern. The ADMINS list is used in error templates and could be injected from the error views; the DEBUG is only used on the status page and could be injected there.

If wer want to make things like ocnfigured admins availlable as a template API for apps, we should provide selective templatetags for it.