Use v4l2 monitor

Use the v4l2 monitor to dynamically add and remove nodes.
Use the info from the monitor as parameter for the factory init and use
it to configure the new node.
Add info to the node.
Use info from the factory as properties on the PinosNode

spa/include/spa/node.h

@@ -154,6 +154,12 @@ struct _SpaNode {
   /* the total size of this node. This can be used to expand this
    * structure in the future */
   size_t size;
+  /**
+   * SpaNode::info
+   *
+   * Extra information about the node
+   */
+  const SpaDict * info;
   /**
    * SpaNode::state:
    *