modify settings loading to separate Django defaults and our explicit declarations

Django 1.7 brought this to light by warning about MIDDLEWARE_CLASSES values changing. I declared it explicitly in our `default_settings` to no effect. This was because I was treating everything as default and Django couldn't tell what was overridden. The treats Django's defaults separately from our Armstrong.Dev defaults, which is probably good to do anyway.
change default MIDDLEWARE_CLASSES to use Django 1.7 default

This will require one change to the `env_settings.py` of some Armstrong components, probably only those that use the Admin though. Since the change only effects component developers?not end users?and is a minimal setting modification?not an interface change or feature removal?it's okay to do in a point release.
do not use the South-based `invoke create_migration` for Django 1.7+
minor packaging and metadata update
project management - use new-style, standard tags for easy deprecation feature searching