Switch to GTK3

[TeofilC]

We upgrade from the deprecated GTK2 to the still supported GTK3.

Most of the changes we had to make were described in the migration guide:
https://docs.gtk.org/gtk3/migrating-2to3.html#changes-that-need-to-be-done-at-the-time-of-the-switch

Many of the functions we depended on for low-level rendering were removed, so I've substituted mostly equivalent ones.

The way events are subscribed to has slightly changed and that has lead to a bunch of changes.

With the new version of GTK3, windows CI works again. Resolves#135, #97

We've also updated the Cabal file to be made aware of stuff included through TH.

[TeofilC]

This compiles but is horribly broken.

For future reference: https://docs.gtk.org/gtk3/migrating-2to3.html#changes-that-need-to-be-done-at-the-time-of-the-switch

[TeofilC]

It looks like the segfaults are now fixed!

[TeofilC]

Windows CI is now working. Nice!

[arrowd]

It'd be great to have this merged in.

[TeofilC]

@arrowd (or anyone else) it would be helpful to have some people test this branch and see if they can spot some issues. If I have some time at ZuriHac, I might finish this off. Hopefully it should just need tidying up. The styling on some things is a bit weird but it should be OK.

[arrowd]

I managed to compile this on FreeBSD, GHC 9.8.4, Cabal 3.14 just fine. Turns out ThreadScope has a number of built-in sample that can be loaded by running it with --test chX with X ranging from 1 to 8. I played with graphs and buttons with the testing data loaded and everything seems fine to me. Hope that helps.

[TeofilC]

I think I'll just merge this as is and create an issue for the remaining styling work.