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.