Support Python 3.8 next to 3.7 and 3.5

[gunterthomas]

I have added python 3.8 support to this branch (maybe in the near future we are able to use newer python versions).
Mostly I built this thing like it can run parallel to 3.5 and 3.7 support - maybe some code is redundant, but I did that on purpose.

If you have anything to improve let me know - this is mainly my first contribution to some really used Open Source Software. If I am missing anything - please comment.

[Ghostkeeper]

I'll warn you that the project to upgrade to Python 3.7 was put on halt for the moment because the main proponent and dev-ops guy that worked on it has left the company. He also didn't communicate/document well what the status was of this project. I don't expect we'll be taking a look at this any time soon.

[gunterthomas]

That's okay, thank's for the answer.
As these changes existed on my local pc anyways while trying to find out what was wrong with cura on Big Sur, I'd simply pushed it to github - as said, it existed anyways - so no worries about that.
Would be cool to contribute some stuff to a software I use day by day, but if it's not needed yet, that is okay.

At least we are not stuck with python2 (as some big players like apple seem to be :D) ;-)

[Ghostkeeper]

:P Yeah we've rewritten the front-end entirely in 2014, and switched to Python 3.4 at the same time, then.