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.
The listeners are generally useful in spa, move it there and rename
to hooks. Implement loop hooks with it.
Fix some cleanup issues in stream and remote
Remove signals.
Rename callbacks -> events, use listeners to listen for events.
Callbacks are still used in spa for things you can listen to only
once.
Make a new method that can take a local node and run it in a remote
pipeline. This basically replaces all functionality of the streams
and more.
Add 2 examples for exporting a sink and a v4l2 node
Make some more things const
Cleanups
Make it possible to do things when the node needs scheduling. The
default node will schedule the local pipeline but the remote node might
also schedule the remote pipeline.
