Read allowed hosts from environment

Recent versions of Django disallow connections with target hosts
not listed in `ALLOWED_HOSTS`. This change separates the hostnames
from application code.
Drop support for Python 2.6

Even Debian is past that and it seems the latest and greatest
Django seems to fail with missing `import importlib`. Not going
to fix this anymore.
Merge pull request #26 from ferrix/master

Support newer versions of Django