Add option to choose the preferred media player in settings

[nielsvanvelzen]

This PR removes the option "Use External Player for Videos" and replaces it with a new option where the user can choose between the following items:

• Auto
  The old behavior when not using external player

• ExoPlayer
  Force ExoPlayer for playback

• libVLC
  Force libVLC for playback

• External
  The old behavior when using external player

A new preference config version is introduced to migrate the existing setting to the new one.

This change could help when debugging codecs in various players and gives the user more control over playback.

[nielsvanvelzen]

I'm not really sure how playback for live tv works and am unable to test it so I did not change those options.

[thornbill]

I noticed some issues when forcing libvlc and the video has to be transcoded:

• Position reporting not updated
• Seek bar does not update on skipping

Maybe we should add some form of disclaimer that this option could cause playback issues if set to exoplayer or libvlc.

[nielsvanvelzen]

So the playback of transcoded video is working but the progress is not updated properly? If that's the only option we should be able to fix that. I'll look into adding a warning when not choosing the auto or external option.

[thornbill]

Right playback is working but when forcing libvlc and it’s transcoding the progress bar does not show the progress and you are unable to resume playback from where you left off. I’m guessing something is up with the progress reporting that is responsible for both of those issues.

[nielsvanvelzen]

I think we should report the progress reporting from libVLC while transcoding in a separate issue from this one so we can fix it after this PR and the ExoPlayer 2 PR is merged. (to prevent conflicts).

Regarding the warning/disclaimer, it seems like it's not possible to add an additional description to list preferences so the only option would be to show a warning after selecting a preferred player. I don't think we should go that far about warning users. We should instead make sure that no matter what playback backend is used their will be no problems.

The only issues I can think of that could happen are:

• Wrong implementation in the library (in this case VLC with reporting the current progress) - This should absolutely not happen and needs to be fixed anyway
• Wrong codec used - Profiles need to be updated so it transcodes

These issues can still happen when the "auto" option is used.