previously, we would only remove the endpoint associated with
the node, but not the monitor endpoint...

to implement that, we now store the node's associated session items
in the node's qdata instead of a local hash table, so that we
can store an arbitrary ammount of session items per node

otherwise the parent never un-exports or de-activates itself
and we leak a bunch of stuff

there is no need to add self in the transition's data,
it's already in source_object

This fixes a failure to activate the monitors if we are using
si-adapter directly instead of si-audio-softdsp-endpoint

Requires PipeWire < 0.3.3 or > 0.3.6 to actually work

In case we have a multi-channel capture device and a mono client,
treat the MONO port as UNKNOWN and let it link with the first
port available on the device

Easy to test with arecord, which by default captures in MONO

it requires GLib 2.60 and it's not worth it

g_object_get_property did not support uninitialized GValues prior
to GLib 2.60, and it's not worth requiring 2.60 for this reason

Fixes #11

this allows slightly easier testing while every client uses node.target
but it's easier to find the endpoint id than the node id
through `wpctl status`

and add the non-disabled filenames in .gitignore so that I can maintain
symlinks to enable them without commiting them

This is out-of-date and we don't need it in fact... the default
configuration can serve as a good starting point for any custom embedded
use case.

if there is a usb device plugged, we can assume it's meant to be used
instead of the built-in audio

jack has the highest prio because if it's present, we assume the
user wants to use jack to route everything

bluez has higher prio than alsa because if it's present, we assume
the user wants to use the bluetooth device

- because it conflicts with pulseaudio and we actually still want
  pipewire to be able to run along pulseaudio on default setups
- and because it doesn't work well yet

replace them with spaces so that the GVariant parser ignores them

We have multiple instances of the monitor plugin, but that's ok.
connect/disonnect will not do anything bad if called multiple times

We need to connect later so that the first connection is the one from main().
Otherwise, if there is a connection error, we will see the warning from the
monitor first.

- pw_core_info has data that represent the remote core
- pw_core properties are the properties of its pw_client,
initially inherited from the pw_context, which can be updated either
when calling pw_context_connect() or later at runtime (the pw_core
calls pw_client_update_properties() on its pw_client)

wp_core_update_properties() is made in such a way so that we can do:
```
clone = wp_core_clone(core);
wp_core_update_properties(clone, ...);
wp_core_connect(clone);
```
and get clone to have different properties than the original core,
while they still share the same pw_context underneath

also delay the "connected" signal until info is there

a method to take the internal pw_properties without copying

and do not allow writing to wrapped pw_properties,
since they are const now

    - due to usage of Reference-counted-data in lib/wptoml/array.cpp
      (requires >= 2.58, see https://developer.gnome.org/glib/stable/glib-Reference-counted-data.html)
    - and usage of G_GNUC_FALLTHROUGH in lib/wp/object-interest.c
      (requires 2.60, see https://developer.gnome.org/glib/stable/glib-Miscellaneous-Macros.html#G-GNUC-FALLTHROUGH:CAPS

)

Signed-off-by: Martin Koch, ESE GmbH <martin.koch@ese.de>