0031649: Visualization, TKOpenGL - broken skybox in VR output

0031649: Visualization, TKOpenGL - broken skybox in VR output

OpenGl_ShaderManager::GetBgCubeMapProgram() and OpenGl_BackgroundArray::createCubeMapArray()
have been corrected to draw cube in straightforward way instead of a screen-quad.

Graphic3d_Camera::SetCustomStereoProjection() now recieves decomposed projection + head-to-eye matrices.
Added method Graphic3d_Camera::StereoProjection() returning projection matrix without translation part.
OpenGl_BackgroundArray::Render() now applies stereoscopic projection matrix in case of VR output,
but keeps using mono projection matrix in case of common 3D displays.