Also fixes a mistake in 229c807c
where isCurrent == isSelected

This fixes #7165 and can be backported.

Several of UI & control plugins follow the volume and mute status
through the playlist instead of the aout. This patch works around
that limitation.

int64_t is not supported natively by the Qt object system.

These helper handle mute (i.e. zero gain) and keep track of the volume
across sessions on a per-output basis. This is intended for the "old"
audio outputs that cannot amplify natively.

This is more flexible than the current approach:
- Gain can be changed if the aout has a custom (native) volume control.
- The callback approach does not break the encapsulation principles
  (so audio_output_t/module_need() could be used somewhere else).

Amplifying dummy is useless. Also amplifying S/PDIF is not possible.

Unknown sections are sections whose name does not match any module in
the module bank. Until now, any unknown section in vlcrc was copied
verbatim when the preferences are saved. In principles, that would
preserve settings for modules that are not available in the current
copy of VLC.

There is a fatal flaw with that approach: When VLC is updated, some
modules may change name. Also some configuration items may be moved
from one module to another. As a consequence, configuration items may
end up in a different section than they previously were. Then vlcrc
will end up with multiple conflicting copies of the same configuration
item: first the current value for the preferences in the new
section, then the old value from the copied old section. When vlcrc is
loaded again, the old copy will override the new one since it is parsed
last. Essentially, the configuration item cannot be changed via
preferences until vlcrc is manually edited or preferences are reset.

I would rather loose settings for old plugins.

Double free was occuring on some psz_url when copying medias.
Might be caused by a double listing from the sql query.

Some crashes occurs on start when processing the first append loop
at the unlock level.