Add mixture legacy/modern QObject::connect()

It would be rather useful to be able to do

connect(foo, SIGNAL(oink), []\{...});

and its counterpart,

connect(foo, &Foo::oink, bar, SLOT(fooOccurred));

This came up with certain declarative use cases - I wanted to connect to signals defined in QML, and would've liked to use a lambda as the "slot". Ulf pointed out that the reverse is also useful, take a native signal, and connect it to a slot defined on the QML side.

thiago, could you take a look, as discussed in the QtCS? I have too many things on my plate right now.