#13 2D focal length and floating point focal point

[Nicolas Mellado]

This is a patch to potentially store different focal length values for x and y coordinates, by converting FocalMm from a scalar to a Point2f.
ViewportPx is also updated from Point2i to Point2f.

Floating values for focal center and different focal length are usual when working with devices such as Kinect.

Core source code + required plugins updated.