Bug 1026184: Port /security to bedrock.

This is nearing completion. I have a question in the bug about what
other pages need porting. It's clear (to me) that some don't.


1. `./manage.py syncdb --migrate`
2. `./manage.py update_security_advisories`

Things should work normally after that.

@jgmize this is decently complete. Some things need more tests, but I'd appreciate a
quick look to at least make sure I'm on a path that will land eventually.

@sgarrity The pages aren't ugly, but could really use your touch, especially the big lists
of advisories.
I think this part of the change should probably go into a separate PR-- that way we could go all the way to production with the rest of the code, validate that everything is working correctly by checking the `/b/security/` URLs, and let @albill verify everything looks good to him before we do anything that affects the current URLs.