pulseaudiosink: Lower rank to prevent autoplugging

pulseaudiosink: Lower rank to prevent autoplugging

pulseaudiosink breaks visualisations in its current form, so let's
prevent it from being autoplugged for the time being.

The best we can hope to do in the 0.10 series is query the list of
available sinks and their formats, and expose these as the bin's sinkpad
caps. While this is not a comprehensive solution, it will make sure that
we're only trying to support compressed formats if we're certain that
one exists.

The long-term fix for this will be in the form of proper upstream
renegotiation support in the 0.11/1.0 series.

https://bugzilla.gnome.org/show_bug.cgi?id=666361