Add script to generate platform keys (.pk8 and .x509.pem)

Signed-off-by: Brandon McAnsh <brandonm@matricom.net>
Add script to generate a keystore from provided platform keys

Signed-off-by: Brandon McAnsh <brandonm@matricom.net>
Add script to sign apk's with requested keystore

Signed-off-by: Brandon McAnsh <brandonm@matricom.net>