Send Intents when PTP compatible devices are connected/disconnected to USB

Usb.ACTION_USB_CAMERA_ATTACHED and Usb.ACTION_USB_CAMERA_DETACHED are sent
when cameras are connected and disconnected.
The data field of the intent contains a Uri for the camera in the Mtp content provider.

Change-Id: I814221b4f0507b309997c71edb5a041e8efc54f7
Signed-off-by: Mike Lockwood <lockwood@android.com>