q4wine: Use system's qtsingleapplication

Gentoo Bug:https://bugs.gentoo.org/show_bug.cgi?id=487540
Upstream Bug: https://github.com/brezerk/q4wine/issues/39
Upstream Commit that fixes it:
https://github.com/brezerk/q4wine/commit/bc30b14b55624b42a5b7c2d603730ea17c919fef