Implement programatic zooming for QtQuick

and add shortcuts in the examples (with a basic UI in the test browser)

Change-Id: I237a04cf0b1fce2e0c6f8a19891ff3cb51727a40
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
TestBrowser: prevent popups from getting GCed

This is a quick fix that only works because dialogs shouldn't outlive
the page that opened them. We still have a problem for the new window
case.

Change-Id: I652e545f7eac394a915f7f173795dc0f187fc6ea
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>