[3D] use GUI stereo mode for video rendering in case we couldn't detect it by stream meta-data or filename
fixup! [3D] move stereomode detection from filename to stereoscopicsmanager and make the flags configurable via advanced settings.
fixup! [3D] add settings to configure the playback behavior of stereoscopic videos

move option "mono/2D" from preferred stereo modes to playback mode spinner where it makes more sense
[3D] make language labels more generic (replace "movie" with "video")
fixup! [3D] add stereo mode popup to Confluence similar to the subtitle popup

always show 3D buttons if stereoscopic support is enabled and add the button also to LiveTV (there are stereoscopic channels, like Sky3D)