bug 1093122 - Drop Python 2.6

Django 1.7 does not support Python 2.6, so we won't either.
bug 1093122 - Upgrade to Django 1.7

Upgrade to pre-release versions of some requirements:

- django-simple-history - includes new handling of OrderWrt
- pylibmc
- django-pylibmc
bug 1093122 - Upgrade additional requirements
bug 1093122 - update to pyroma 1.7

pyroma 1.6 exited with status code 1 on success, pyroma now exits with
status code 0, so Makefile check updated.
bug 1093122 - Fix license in setup.py

The license should be ignored when there is an applicable classifier,
but still it should be MPL 2 and not BSD.
bug 1093122 - Remove unneeded autodiscover()
fix bug 1093122 - Add migrations