Enable postscript printing again

Could you add postscript support again to QPrinter? Why was this removed in Qt 5? I think this is a format wtill heavily used, as it is one of the few vector formats that one can use with for instance MS Word.

One possible solution is to provide this in a similar way to QPdfWriter, that way it can be used directly (QPostscriptWriter) or via QPrinter::setOutputFormat() too.