[3D] expose stereomode to skins via ListItem.StereoscopicMode and ListItem.IsStereoscopic
[3D] add stereomode flags to Confluence
[3d] default the RENDER_STEREO* enums to 0
[3D] ensure m_StereoMode/Invert are initialized in the constructor
[infomanager] GetItemBool() should use the window's listitem if none is present
[infomanager] no need to special-case ListItem.IsPlaying et. al. to be multi-info bools now that GetItemBool will work with them