Power menu: Update Silent/Sound mode button:

On devices with vibrate function, (tri state button):
- Set 100% opacity only to the icon which represents the current state

On devices without vibrate function, (toggle button):
- Change button from silent mode to sound mode:
  - Change icon from audio mute to audio

Toggle button:
Reading the code possibly leads to some confusion,
because the sound mode button code is still called "silent",
I`ll change this later.