Maintain middleware related to security headers.
Maintain middleware related to security headers.

* Remove outdated `commonware`
 * All functionality available in Django
* Add native Django HSTS support
* Remove unused cookies middleware
 * We already use SESSION_COOKIE_HTTPONLY, SESSION_COOKIE_SECURE

fxa90id/mozillians,mozilla/mozillians,akatsoulas/mozillians,johngian/mozillians,johngian/mozillians,mozilla/mozillians,mozilla/mozillians,mozilla/mozillians,johngian/mozillians,fxa90id/mozillians,akatsoulas/mozillians,fxa90id/mozillians,fxa90id/mozillians,johngian/mozillians,akatsoulas/mozillians,akatsoulas/mozillians