added environment-variable-based DATABASE config

This way, DATABASE settings don't need to be changed in settings files
that extend settings/base.py, unless said child settings wish to change
the database engine from PostgreSQL to something else.
commented out aacc-django-common apps by default

These should be enabled as necessary for a given project.
moved collected-static and upload dirs to httpdocs

This creates a more logical separation between non-collected static
files and collected static files, and, since these projects are likely
going to be placed in /var/www/vhosts subdirectories, having files that
should be served directly by Apache in a directory called 'httpdocs'
makes a lot of sense.
added settings/{dev,prod}.py

These settings are used for development and production. While most
everything that would change between development and production is
controlled via environment variables, this separation gives us a little
more flexibility.
updated readme