Merge remote-tracking branch 'refs/remotes/origin/QtGUI' into QtGUI

diff --cc announcer/window.py
index 0d17a34a4d5cb93e21a03ffce455a94792520c1b,cc4641536fb2922066f4c0dce7fe3d897b42f86f..8e45f8ca8caa312e8ab1559d5a4e6a519a250036
--- 1/announcer/window.py
--- 2/announcer/window.py
+++ b/announcer/window.py
@@@ -35,9 -35,11 +35,11 @@@ class MainWindow(QtWidgets.QMainWindow)
          self.volume_slider.setRange(0, 100)
          self.volume_slider.setValue(50)
          self.mute_button = QtWidgets.QPushButton("Mute")
+         self.is_muted = False
+         self.previous_volume = self.volume_slider.value()
          self.test_volume_button = QtWidgets.QPushButton("Test sound")
 -        self.headerlabel = QtWidgets.QLabel("Hello World")
          self.volume_level_label = QtWidgets.QLabel("Volume: 50%")
 +        self.volume_level_label.setAlignment(Qt.AlignCenter)
          self.packlabel = QtWidgets.QLabel("Sound Pack:")
          self.sound_pack = QtWidgets.QComboBox()
          self.sound_pack.addItems(SOUND_PACKS)