This triggers e.g. haptic feeback as well and can later on be used
for LED feedback.
We can drop the audio theme setting completely since feedbackd picks up
the global GNOME setting.
Since feedbackd currently does not cancel gsound's via a cancellable
this might make the phone ring a bit too long atm but that will be fixed
on the feedbackd side
(https://source.puri.sm/Librem5/feedbackd/-/issues/10)
How `g_type_class_peek ()` was used it didn't return the correct parent
class in most cases.
G_DEFINE_TYPE macro creates a pointer we can use to get the parent
class `n_p_parent_class`.
Because we didn't use the correct parent class the object initialisation
wasn't fully completed for some GtkWidgets.
See https://developer.gnome.org/gobject/stable/chapter-gobject.html#gobject-instantiation
for more information.
This commit makes use of the `n_p_parent_class pointer` created for this
specific use case where ever possible.
Fixes: https://source.puri.sm/Librem5/calls/issues/118
