Templatetags and Import Refactoring for Python 3

• Replace django-templatetag-sugar with native Django tags
• Use relative imports

Fix a few deployment errors

v2.1

Fix events.js link in HTML

Dokku Release

Configuration has been rewritten to a 12-factor application, and has been deployed to Dokku.

Final Django upgrade in release cycle

Upgrade to Django 1.8.15. Cannot upgrade any further without a rehaul of our use of django-templatetag-sugar, which is incompatible with the loader system in Django >1.9. Django 1.8 will continue to have support until April 2018.