[bluray] Add a setting for preferred bd playback 

The options are

~~* default : current situation: index.bdmv ==> main title, MovieObject.bdmv ==> simplified menu~~
* "play main movie"
* "show disc menu"
* "show simplified menu"

The default option could be dropped.

Furthermore bluray directories are "opend/played" the same way as discs/images (but via context menu)
thx @da-anda and @Voyager1 for the help!