Since 9d612ff1c7 this is required,
otherwise we never set up the GtkAdjustment and so the scales don't
display any values or widget to make adjustments, meaning they can't be
used.
Also call `notify_volume_cb()` from `update_ranges()` to initialise the
adjustment, since when we set the mixer control we now might not have
set the value.
Closes#652
The current code does not differenciate between input and
output, and thus it shows the same icon for muting outputs
and inputs. As per design suggesion [1], the input row
should use the "microphone-sensitivity-muted-symbolic" icon.
In order to achieve that, move the CcLevelBarStreamType enum
to a separate header, and rename it to CcStreamType. And also
pass the stream type to the volume slider.
In CcVolumeSlider, update the code to switch to the correct
mute icon depending on the stream type.
[1] https://gitlab.gnome.org/GNOME/gnome-control-center/issues/539
Fixes https://gitlab.gnome.org/GNOME/gnome-control-center/issues/539
