[3D] default preferred stereoscopic mode to "auto"
[3D] use ENUMs for playback mode
[3D] make "mono/2D" a default playback mode instead of a preferred stereo mode (it's no real stereomode)

Also removes the mode "none" from the list of preferred modes, and moves it to the playback modes.
[3D] hide stereomode of movie in ask dialog if preferred mode is sames as movie mode
[3D] show "same as movie" as preferred mode label in case of autodetection instead of the detected mode
[language] cleanup and improve stereoscopic labels

- removes duplicates
- makes wording more userfriendly
- adding contextual help string for stereoscopic related labels
[confluence] adjust size of OSD 3D balloon dialog label to match new string length
[3D] support AUTO mode to GetLabelForStereoMode()
[3D] add missing return values after action handling
Merge pull request #5236 from da-anda/3D-ux-fixes

[3D] usability fixes and cleanup