Change _.super to _super.

I just submitted an equivalent change to the reviewboard code-base, so this
needs to be updated, too. Trivial change.
Fix issues with rbdemo on a production server.

rbdemo had a couple issues on a production server. First of all, the
package didn't contain the management commands, and depended on
ReviewBoard (which can cause problems).

Second, resetting the demo server ended up putting things in a bad
state. We didn't have the right permissions and ownership for media
files.

This change fixes these problems. There may be more issues that I'm
still investigating.
Filter stuff out from the demo database when dumping/resetting.

rbdemo now filters out a bunch of stuff we don't want to keep in the
dump file. This includes guest user entries, review request visits,
the siteconfig, and unwanted extension entries.

When loading, we preserve the old siteconfig so that we don't end up
with stuff from a development server overwriting the stuff on
production.