Add signal handlers for daemon to shut down
Add destroy listeners for modules and do cleanup
Fix some leaks
Simplify port registration in new nodes
Hide some more data structures
Let the node implementation take care of the reuse_buffer signal because
then we can get to the graph nodes to find the destination port.
Destroy modules in core cleanup. Modules should undo everything they
have done.
Activate the link after we negotiated format and buffers.
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.
