Qt-GTK3 - attempt at creating distinct package for platform plugins

[hmaarrfk]

I guess I would love to be able to build this as a distinct package.

Using inspiration from qt's own move to CMake and Fedora's packages to create a cmake file

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[conda-forge-webservices]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipes/qt-gtk-platformtheme) and found it was in an excellent condition.

[hmaarrfk]

@jschueller any comments here? I know this is a heavy handed approach, but I'm just trying to make the best a challenge packaging.

[hmaarrfk]

My goal would be to merge this weekend.