RFC: lib: media_player: add a config struct

On top of !3503 Please only review the last commit.

I will close this MR once I have your feedbacks (and include it or not into !3503).

I added a configuration struct for the media player, for now it can only disable/enable the osd. This may be used later to all kind of options.

The big advantage:

• Just increment the version and add a member to the struct instead of adding 2 new functions : getter and setter
• These options can only be set before creation, so we don't have to handle change in the middle of a playback
• No extra allocations (hence the public struct and version), pass NULL for default configuration
• Could be used to handle more vlc options, in a more restricted and controlled way

I suggest adding nsobject/xwindow/android/hwnd surface configuration in this struct. Is there a reason to handle more than one kind of surface ? Is there a reason to allow a surface modification while playing ?