[Development] Switch the main "Qt Build System"

[Edward Welbourne]

Alexandru Croitor (9 June 2020 10:41)
> I'll acknowledge that the current Qt Creator <-> Build Qt with CMake situation is sub-par.

Is there a P1 ticket open about that ?
Might even warrant P0, given ...

> We have to bite the bullet at some point.

In particular, the "Structure and platform freeze" at the end of June is
only three weeks away.  I'm guessing we need Coin migrated to CMake by
then.  We need CMake to be the usual mode of development by then.
Notably including: for those using Qt Creator ...

	Eddy.