Externalize QuerySet builder.

[bryanhelmig]

In addition, this should make the base not tied to User, but instead selectable off of something in the ContentType framework.

[bryanhelmig]

Meaning, the QuerySet builder might make a nice, totally separate pluggable Django app.

[SkinTeam]

This would be killer, we're not yet on 1.5, so we're rather limited in what we can do with this at the moment.