mate-accessibility-compiz: play_sound_restore_volume.sh: rewrite it

completly to avoid sound reduction with PulseAudio. Previously, when
the sound was inferior to the default one, the sound of others
clients (eg. speech-dispatcher) was reduces each time the bell was
played. With this new implemtnation, the bell sound is played at the
volume level so avoid impact on the PulseAudio sound.