[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!

at least to me it's not clear - it could also mean among other playback modes? But that's probably just me not being a native speaker. As said - it's just a nit pick and really not that important.