Clean up several aspects of the models

Review Request #436 — Created July 4, 2008 and submitted — Latest diff uploaded


Review Board SVN (deprecated)


Cleaned up some of the models by giving all relationship fields explicit related_name fields, rather than using Django's pre-generated defaults. This makes for more natural names and is something we'd want to do before extensions land later on.

This also moves error types and the custom Manager in reviews to their own files.
All unit tests pass.