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/client-port.h

@@ -30,6 +30,7 @@ typedef struct _PinosClientPortPrivate PinosClientPortPrivate;
 
 #include <pinos/client/introspect.h>
 #include <pinos/client/port.h>
+#include <pinos/client/client-node.h>
 
 #define PINOS_TYPE_CLIENT_PORT                 (pinos_client_port_get_type ())
 #define PINOS_IS_CLIENT_PORT(obj)              (G_TYPE_CHECK_INSTANCE_TYPE ((obj), PINOS_TYPE_CLIENT_PORT))
@@ -66,6 +67,10 @@ struct _PinosClientPortClass {
 /* normal GObject stuff */
 GType               pinos_client_port_get_type           (void);
 
+PinosClientPort *   pinos_client_port_new                (PinosClientNode *node,
+                                                          gpointer         id,
+                                                          GSocket         *socket);
+
 GBytes *            pinos_client_port_get_formats        (PinosClientPort *port,
                                                           GBytes          *filter,
                                                           GError         **error);