I don't think it's needed anywhere in QGC since this has been a bug for a long time.

SLUGS has maintained their patches out-of-tree for a long while now.
These will eventually get merged back in, but it'll be easier to evaluate them as fresh commits instead of modifications to this old & dead code, so we'll delete this for now.

Some functionality was lost, will need to be fixed in a later commit.

To include OpenGL primitives, we include the QtOpenGL header instead, which has all the platform-specific includes taken care of for us.

Also added selection from tree view for downloading