Rework how clients connect.

Add buffer flags. The idea is to make it possible to easily check when a
buffer contains control information that we need to parse to update the
port fields.
Make the client create remote nodes and ports and set up proxies for
them.
Make a port base class implementing most of the logic to pass buffers
locally and remotely.
Remove most code from stream.c, it's now in the port.
Make a portsink and portsrc that can write and read to/from any port. We
use these in the server to send and receive data.
Rework format negotiation. The final format is now sent in-line before
the data. The server will select a format on output ports.

pinos/client/node.h

@@ -79,6 +79,10 @@ struct _PinosNodeClass {
 /* normal GObject stuff */
 GType               pinos_node_get_type                (void);
 
+const gchar *       pinos_node_get_name                (PinosNode *node);
+PinosNodeState      pinos_node_get_state               (PinosNode *node);
+PinosProperties *   pinos_node_get_properties          (PinosNode *node);
+
 void                pinos_node_remove                  (PinosNode *node);
 
 void                pinos_node_create_port             (PinosNode          *node,