Database self check does not play nice with fake data

[zbynekwinkler]

We have merged #1768 but fake_data does not respect all the relationships that are checked in the self check. Current workaround is to not run the homepage updater thread by putting UPDATE_HOMEPAGE_EVERY=0 in local.env.

One way to go forward with this would be to use our own data creation functions. Maybe something similar to make_participant in testing harness? This would also help our javascript testing as we could make fake_date less random (use 'alice', 'bob' and 'carl' just as in python unit tests).

[Changaco]

Closing in favor of #2600.