Add default board to new projects, remove uncategorized pseudo-board (#29874)
On creation of an empty project (no template) a default board will be
created instead of falling back to the uneditable pseudo-board.
Every project now has to have exactly one default boards. As a
consequence, you cannot unset a board as default, instead you have to
set another board as default. Existing projects will be modified using a
cron job, additionally this check will run every midnight by default.
Deleting the default board is not allowed, you have to set another board
as default to do it.
Fixes #29873
Fixes #14679 along the way
Fixes #29853
Co-authored-by: delvh <dev.lh@web.de>
Denys Konovalov