Porting of KTechLab to Qt6/KF6 started

[Zoltan Padrah]

Hi,

I have started the porting of KTechLab to Qt6/KF6; an initial version
that compiles can be found in the `kf6-v0` branch :

https://invent.kde.org/sdk/ktechlab/-/tree/kf6-v0?ref_type=heads

Any help with making the new version usable is welcome.

The current status is:

This port builds and the application starts up, but it crashes when
closing the application or when closing any document.
The examples menu shows invalid entries.
I have also seen some warnings in the console, probably those would be
nice to fix, too.

Besides fixes, testing would be also very useful, to have a list of
know issues (and those to be fixed at some point).

Have fun,

 Zoltan