* Every client has a priority based on its role
* For playback, we allow only a single client to play at a time
* For capture, we allow all clients to capture simultaneously
* Every time the "selected" device changes (either because devices
  are discovered/removed or because the user changed the selection),
  the clients are re-linked to the new "selected" device.
* When a playback client quits and there are others waiting unlinked,
  the highest priority one is linked automatically.
* This also properly fixes re-linking the correct client(s) to the
  correct device(s) when wireplumber exits and restarts.

Fixes #1

signal emission apparently does not work in _finalize()

Fixes some critical warnings from remote-endpoint.c because disconnection
from the destroyed endpoints did not happen

This avoids being able to find the same object on the globals list
from code that is connected to the signal.

avoids criticals and crashes when the core is destroyed earlier

+ add a method to retrieve the core
+ change the register function to not require the core as a parameter

This is a cleaner way to interface with the remote pipewire daemon.
The WpRemote base class can be subclassed also for interfacing
with other daemons (hardware-specific managers, etc)

This can be used by code that depends on policy to re-evaluate
choices they have made in the past that could now change based
on the new policy.

The core may be the last object holding a reference to the endpoint,
so the unregister call may destroy it.