m-config-static-nodes: remove unneeded 'conected' callback and create static nodes when the plugin is activated

This module suspends a node if idle for at least 3 seconds

* Use a direction instead of a string prop id
* Emit default-endpoint-changed again
* Get rid of the useless virtual methods

+ rename FEATURE_CONTROLS to FEATURE_PROPS
+ add accessor for the standard spa_param_info (info->params)
+ hide the low-level params API that nobody uses

-> wp_trace_boxed (WP_TYPE_SPA_POD, pod, "some message");

by using G_TYPE_NONE (== 1), we can pass this in the log handler
to point out the fact that we expected something but it's null

As a bonus, a null object always gets printed in red because that's
the first color in object_colors

Disconnecting core finishes all pending tasks, which is needed in order to avoid
possible leaks if some tasks are still pending when exiting.