Make real spa_graph nodes and ports and schedule those. This makes
it possible to add explicit tee and mixers in the real graph.
Rework the way we add and remove ports and nodes from the graph.
Remove confusing pw_port_link and merge core with pw_link_new()
Move scheduling in separate files, add some more graph-schedulers.
Add version numbers to protocol interfaces and implementation.
Allow allocating user_data in proxy and resource
Use separate methods to set implementation.
Add protocol object to keep track of available protocols and
interfaces. Add possibility to dynamically register interfaces.
Make a default logger and mapper in a .h file to be used by examples
Remove logger and mapper from libs
Make method to set the default mapper for the debug methods
