Acess by name infrastructure

fixes based on the feedback: window name prefix is automatically added when it is not there, singleton class returns reference instead of pointer, destructor is private, release function implemented

initial shared pointer implementation for Viz3d, singleton VizAccessor, cv::viz::get function initial implementation

Implementing camera

principal point is always set even though the intrinsic parameters are not given (center of window), fixed computation mistakes in setWindowSize in camera class

initial implementation of projection matrix, 3D to window coordinates, window coordinates to 3D ray (not yet tested)

Implementing widgets