I think this is a big improvement in readability.
I removed the `lnav` config, which is a little sad, but I don't think it
supports this structured logging format well. Still seems worthwhile on
balance.
- after 3->4 upgrade, it left the foreign key referring to the
nonexistent old_camera table. Likely no one who did the upgrade
has ever inserted anything into this table, so no one's noticed.
- 6->7 upgrade dropped tables in the wrong order, so if there was
anything in the signal_camera table, the upgrade would fail.
Now there's room to add arbitrary configuration to signals and types.
Several things are no longer fixed columns/tables but instead within
the configuration types.
