Port mldonkey GUI to GTK3

[XVilka]

GTK 2 is being deprecated, and there is largely compatible version of OCaml bindings to GTK 3 is available - lablgtk3.

See lablgtk3 branch here: https://github.com/garrigue/lablgtk/tree/lablgtk3

[a17r]

Are there any plans? GUI will soon need to be dropped from packaging.

[ygrek]

I don't have immediate plans to work on this. Do you have any estimate how many users use/install gui package?

[a17r]

I actually have no idea, nor how important it is for users to have a UI at all - I'm just not aware of any alternative in our package tree, kmldonkey was dropped 3.5 years ago already.