Sorry this commit is so large...  I changed user uploaded content to be related to atoms via a ManyToManyField like submissions.  I changed the category structure to use parent_categories instead of child_categories when the user defines them.  I made a lot of changes to web.models to make it more consistent.  I still need to fix the admin site and reimplement the video viewing feature.
Fixed topic voting, added two files I forgot to put in the last commit.