QbsProjectManager: Set up Qt version numbers.

This was simply forgotten, leading to semi-random behavior in the
profile setup code (e.g. a Qt 4 version being treated like a Qt 5 one).

Change-Id: I6d75cf3c622a0dd520724b25eb9b823d3dcc117d
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>
Reviewed-by: Jake Petroules <jake.petroules@petroules.com>