Device Selection re-uses the local video track for its preview.
When displaying Device Selection while video muted, the text
"muted" displays within the video preview, but some translations
may mistake this to mean audio muted. The text has been changed
to be explicit about video mute. This is a temporary solution;
at some point Device Selection should not re-use the local track
except for IE, the one browser that cannot get multiple tracks
from the same video input.

The Device Selection modal consists of:
- DeviceSelection, an overly smart component responsible for
  triggering stream creation and cleanup.
- DeviceSelector for selector elements.
- VideoInputPreview for displaying a video preview.
- AudioInputPreview for displaying a volume meter.
- AudioOutputPreview for a test sound output link.

Store changes include is primarily storing the list of
available devices in redux. Other app state has been left
alone for future refactoring.