This gets rid of most of the djblets.util.compat.django code, and

updates all call sites to use the versions available in Django 1.11+.

Mostly, this is template-related code or management command code.
There are some changes in behavior for template code, functionality

differences around contexts that the old compat code papered over and

now needs manual changes. Mostly this involves calling

context.flatten() when calling render functions.

Unit tests pass on Django 1.11.