Remove the memory stuff from the spa API, we can do thing more simple
and efficiently if we always allocate buffers outside of the plugins and
only implement an alloc function on the node when it can do something
clever.
Move serialize code to the props/format/buffer code
Make it possible to copy a format and properties.
Make events and command specific to the node
Remove some unused code
Improve state changes
Use easier fixate by just taking the element default value
Fix reuse buffer in the proxy
Work on idle poll
Move node state to the node interface so that we can actually get it in
the sync case.
Add enabled field to the poll event
Work on audiotestsrc
