rbdemo has always been a bit hard to maintain. We relied on Django's

fixture support to dump out state and load it in, and this doesn't

really work well when moving between versions of Django or Review Board.

It's also just really hard to maintain the data we want to put up.
This is a complete redesign of how we deal with state for rbdemo.
First, safety. We no longer use Django's management commands to reset

database state. These run in, and commit, their own transactions,

meaning that if we fail to load state after we reset, we just end up

with an empty database.
We now handle the flushing/resetting process ourselves, but more

selectively. Tables essential to running the server (site, siteconfig,

evolutions, migrations, etc.) are kept intact. This also makes it much

easier to set up a mock demo server for development.
Everything is now run in a single transaction. If anything goes wrong,

we shouldn't lose anything already in the database. This makes periodic

resetting safe.
The idea of how we load data has also been entirely redone.
We no longer use Django's fixtures support. Instead, we load a YAML file

(or files) that contains basic structured data needed to populate a demo

server. This is easier to maintain, as we can just edit some content in

the files and re-import into a demo server.
Since we're in full control of the loading process now, and are less

tied to exact database state, we should have a lot fewer problems

updating this as we upgrade Review Board.

Tested reloading demo data with errors. The server no longer had to be

reset.
Built a YAML document containing all the content from demo.reviewboard.org

and have successfully been able to import it, edit it, and re-import it

numerous times. The content on the server fully matched expectations.