overloaded Intrinsics::loadProjectionMatrix with viewportRect argument

In some cases (projection mapping, use of external display..etc) it can be useful to set the viewport coordinates and size. This PR just adds an overloaded method with the viewport as first argument.

EDIT :  in case of projection calibration, the imageSize is likely to be different from the camera input size used to detect the calibration pattern. So I also had to add a setter on Intrinsics::imagSize