Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

It only works for blend and X mode but there are probably the most used.
When blend/X are enabled/disabled:
 - It avoids recreating the vout.
 - It avoids deinterlacing the (soft) subtitles.
The other modes are not possible without a lot of vout works, so it is
postponed for later.

As a side effect, the initial value of the menu now takes into account the
command line options.

Please, report any regression. This code is made complicated by the
vout filter/video filter2 switches&tricks.

The current code assume it everywhere.

It now supports I422 and discard mode.

It is only used from a single thread

And hmm, this really should use a condition variable too.

That is the same problem as we already had with other object types.
The interface really needs to unload when its owner stops it, not when
the reference counter drops to zero. This fixes a reference dead loop
when an interface yields itself (such as Qt through the view menu) and
a crash if an interface releases itself last (unmapping the running
caller code).

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>