Use the right template context processors on Django 1.11.
Use the right template context processors on Django 1.11.

Django moved their core template context processors into a new module
in 1.8. This updates our settings to pull in the right context
processors for both Django 1.6 and 1.11.

Testing Done:
Unit tests pass on Django 1.6 and 1.11 (with other in-progress changes).

Reviewed at https://reviews.reviewboard.org/r/10526/

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