There will be designated classes for audio and video

When rendering in Direct3D11 to NV12 we use 2 planes in the same texture.

In order to use several different ctx from main().

No functional changes.

Regression from ad183c8f

It would have been used as NULL otherwise

and better handling of leaks

It need to be ported to the new player, playlist and tree.

The vout is now always present, there is no need to use the old playlist as a
proxy.

IMPORTANT: the video filter settings will now only change for the main vout. We
need to define a way to change vout settings for other windows.

The aout is always present, there is no need to use the old playlist as a
proxy.

Since the vout is now persistent, there is no need to store the variables on an
intermediate vlc_object_t (that was wrongly set to the interface during the
last UI merge).

IMPORTANT: the video filter settings will now only change for the main vout. We
need to define a way to change vout settings for other windows.