USB accessory support library

This provides a mechanism for developing applications to work with
USB accessories in versions of android prior to the introduction
of the android.hardware.UsbManager APIs.

Applications should link against the com.google.android.usb library
to use this support.

Change-Id: I48ff80467fd9a6667aa84a758eca754132f546b9
Signed-off-by: Mike Lockwood <lockwood@android.com>