Clean up USB notifications:

Add support for separate USB connected and configuration events

Include both USB connected/disconnected and configuration state
in USB_STATE Intent

Remove redundant USB_CONNECTED and USB_DISCONNECTED Intents
Now we just have the sticky USB_STATE broadcast

Move USB disconnnect rebouncing from Tethering to UsbService

Change-Id: Id13eb0c5d51152d2a538985d680ba1db7d2241dc
Signed-off-by: Mike Lockwood <lockwood@android.com>