[apps/qglviewer] using paintGL/initializeGL instead of QGLViewer's init()/draw()

QGLViewer is an OpenGL2 application, but we are "abusing it" for OpenGL4.
Therefore, to avoid errors, I just use paintGL/initializeGL
[GL] added ortho matrix generator to Eigen support
[GL] format and widget for OpenGL 3.2 context (highest supported in cross-platform)
[apps/qglviewer] ability to enable/disable qglviewer in favor of qglwidget