minimal implementation of ^Y

[CapelliC]

I was hoping that QShortcut could attach the event without any change in the keyboard handler. It was not the case.

[JanWielemaker]

Thanks! Looks fairly similar to the swipl-win version. Except that it does not put the closing quote there and if there is no opening quote it does not put the opening ' there. It also escapes the quote by doubling it. The others put a backslash before it. Both are legal, but I consider doubling more backward compatibility. I'd rather get rid of it, so we could add """long string""" syntax.