... and make WpIterator Lua-friendly so that it can be used
with the generic for loop

Fixes #20

a module that allows loading and executing Lua
scripts from a configured directory

Now the WpPipewireObject interface is directly implemented by the mixin
and there is another interface that users of the mixin must implement
in order for the mixin to work proprely.

A lot of manual stuff that proxy classes had to do before are now
in the mixin. Also most of the data that would normally reside in Private
structures is now in the mixin data structure (stored as qdata on the object).
This is achieving the best amount of code reuse so far.

For impl objects (WpImpl*) there are also default implementations of the
standard pipewire object methods and the INFO & PARAM_* features are
more coherently enabled during the whole lifetime of these objects.

A callback is required, NULL is not accepted by GCClosure

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

The Dbus device reservation has been moved into a separate module, and has also
been refactored to allow reserving a device name before an actual device is
created. Devices now are created and destroyed by the monitor depending on
whether PipeWire owns the device or not. This also simplifies a lot the device
activation module to always enable devices when they are created, and never
worry about checking whether a device is acquired by PipeWire or not.

Allows implementing device specific endpoint creation logic, which is currently
needed for bluetooth endpoints as they need to be created differenly.

there are underlying issues with the state management of the graph,
so it's not a very good idea to rely on it to activate / deactivate
our convert node depending on the links that exist

instead, track the links ourselves and create/destroy the corresponding
links to the target node accordingly; it's a more robust approach

it was also not entirely correct that we would previously configure
the convert node to be a driver (node.driver=true); maybe this caused
the underlying issues in the first place... we don't need it now
anyway, so it's gone

Just like media-session does
JACK nodes should be left untouched

1. device export proxies must be destroyed manually since they are
   not associated with the WpRegistry
2. the monitors should not disconnect before all WpSpaDevice objects
   are destroyed; remove the manual disconnect call and let GObject
   ref counting do its job (the core will disconnect when its last ref
   count is dropped after the last monitor plugin is destroyed)

* do not copy the full alsa node properties set
* use a node description that makes the nodes look better in JACK
* use . instead of / as a separator for the node.name, like elsewhere
* add audio.convert spa lib association in the tests that use si-convert;
  previously it used to work because library.name was present in the
  properties copied from the adapter (and it so happens that the adapter
  lives in the audioconvert spa plugin as well ...)

JACK uses : as a separator to distinguish the port name
from the node name, so it ends up doing wrong separations
if we have : in the node name

This may happen if the plugins were loaded but not activated
due to some parse error in wireplumber.conf

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

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