Comment 0 for bug 1389099

When we press mic mute key(in some HP's notebook, it's Fn+F8), the notification shows sound mute icon, not mic mute icon.

My investigation:
In the file: gsd-media-keys-manager.c, there's no icons[] array for mic mute, there're only volume_icons, brightness_icons, kb_backlight_icons. we have to add mic volume detection to ubuntu_osd_notification_show_volume().

Also we need icon files for mic mute. File name should be something like notification-mic-volume-muted, notification-mic-volume-low, notification-mic-volume-high.