Spooling up a full PLAYER in the background takes too long.
This also fixes bugs around how the tables are saved, although
that was just missing code rather than anything architectural.
Fixes: lp:1785436
* https://bugs.launchpad.net/kicad/+bug/1785436
This also fixes a bunch of bugs where an error during save would
still close the window (rather than cancelling the close action).
Fixes: lp:1785034
* https://bugs.launchpad.net/kicad/+bug/1785034