The playsink was nastily poking a boolean in the structure.
Make those booleans properties, so we are told when they change,
and rebuild the conversion bin when they do.
Some cleanup to go with it too.
https://bugzilla.gnome.org/show_bug.cgi?id=661262
The code was doing counterintuitive rewiring of pads when the
bin did not contain any elements. We now add an identity element
in that case, which makes it simpler, and should fix the AC3
passthrough mode when using pulseaudio (but I don't see the bug
here so can't test).
https://bugzilla.gnome.org/show_bug.cgi?id=661262
These reconfigure based on the caps and plugin in converters if
necessary. This also makes switching between compressed and raw
streams work flawlessly without loosing the states of any element
somewhere or having running time problems.
