USB connected notification and temporary USB options dialog

This change adds a notification when USB is connected.
Selecting the notification brings up a dialog to allow switching between
MTP and PTP modes, and also allows mounting a CD image for installing AFT.
The UI design is not final - this is a temporary implementation of the UI.

Change-Id: Idd678537aba595fd4cb183ea755bf437f372d826
Signed-off-by: Mike Lockwood <lockwood@android.com>