Avoid duplicating API, remove implementations from port and node and
always use an spa_node as the implementation, it's just as easy to
implement a spa node. With the implementation always being a spa_node
we will be able to better implement the negotiation of the mixers.
Add some callbacks to trigger push and pull in a graph
Remove the scheduler, make some implementations of graph push/pull
functions.
Add some properties to jack clients and nodes
Fix the parent of the clients.
Notify link format changes
