Move away from django/test-utils.

Django test-utils is outdated. We are moving a few things into our own
test setup and switching to Django's test cases.
Allow anonymous users to validate hosted apps (bug 1090341)
Merge pull request #2685 from mstriemer/anonymous-hosted-app-validation-1090341

Allow anonymous users to validate hosted apps (bug 1090341)
handle feed items in ES that don't have feed element data (bug 1088001)