Use LEDs of simple interface to show client state

[esilky]

The simple interface currently indicates when the client is listening and when it is responding (using the blue LED). The simple interface includes a red and a green LED that can be used to indicate other status of the client.

The suggestion is that the following indicators be used with the simple interface:

• Solid red: Client is muted (not listening or playing)
• Blinking red: Client does not have a server connection and is trying to connect
• Solid blue: Client is listening (after wake-up)
• Blinking blue: Client is playing response
  (green is currently unused)
  The simple interface assumes the use of a single RGB LED, such that a full hue of colors can be displayed. This might be used in the future to display various status. This will not work well if the simple interface is constructed using three separate LEDs (red, green, and blue).