audiosink: expose more audioringbuffer vmethods to child sinks

audiosink: expose more audioringbuffer vmethods to child sinks

The newly exposed vmethods are pause, resume, stop and clear_all.
The existing reset vmethod is deprecated.

The audio sink will fallback to calling reset if pause or stop
are not provided and will fallback to calling start if
resume is not provided. There is no default clear_all
implementation.
Existing audio sinks continue to work as before.

This change is useful for sinks that need to distinguish
between a pause and a stop (currently both are handled
by a reset) and is needed for https://bugzilla.gnome.org/show_bug.cgi?id=788362

https://bugzilla.gnome.org/show_bug.cgi?id=788361