Disable m-session-settings for now, as it needs further work

By mistake, WpImplNode was developed by keeping in mind that the proxy
returned by pw_core_export() is a PW_TYPE_INTERFACE_Node, but this
is not true. It's actually a ClientNode...

Unfortunately, making WpImplNode work as if it was a WpNode is
not so easy, especially when it comes to handling params, which
need to be queried syncrhonously on the underlying spa_node.

So, instead of fixing WpImplNode to work as a WpNode, we choose to
disconnect them. This way, WpImplNode will not be used as a proxy
in the registry and the registry will normally create WpNode proxies
instead, making round-trips through the server to change node params.

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

This will solve a possible race condition in the unit test when destroying the
autotestsrc proxy while its node_event_info is being called.

There are 3 kinds of WpProxy objects:
 * the ones that are created as a result of binding a global
   from the registry
 * the ones that are created as a result of calling into a remote
   factory (wp_node_new_from_factory, etc...)
 * the ones that are a local implementation of an object
   (WpImplNode, etc...) and are exported

Previously the object manager was only able to track the first kind.
With these changes we can now also have globals associated with
WpProxies that were created earlier (and caused the creation of the global).
This saves some resources and reduces round-trips (in case client
code wants to change properties of an object that is locally
implemented, it shouldn't need to do a round-trip through the server)

* core no longer exposes create_remote/local_object
* node, device & link have constructor methods
  to enable the create_remote_object functionality
* added WpImplNode to wrap pw_impl_node and allow creating
  "local" node instances
* added WpSpaDevice to wrap spa_device and allow creating
  "local" device instances
* exporting objects in all cases now happens by requesting
  FEATURE_BOUND from the proxy, eliminating the need for WpExported
* replaced WpMonitor by new, simpler code directly in module-monitor
* the proxy type lookup table in WpProxy is gone, we now
  use a field on the class structure of every WpProxy subclass
  and iterate through all the class structures instead; this is
  more flexible and extensible

This module allows wireplumber to create static nodes that match a specific
device using a spa node factory. Matching is optional, and if there is no match,
the node will always be created.