Key forwarding and single app mode update

Added new code for keyboard device injection, now receives
messages from svmpd and creates/destroys virtual input devices.
Simplified SVMP hooks' broadcast receivers, now utilize
SVMP_BROADCAST permission when sending/receiving broadcasts
as appropriate.
Removed some unnecessary protected broadcasts.
Fixed notification broadcast issue where user notifications would
not get properly sent.
Added more comments to clarify where SVMP hooks are.

Co-commits:
android_device_mitre_svmp
android_external_svmp_eventserver
svmp-android-client
svmp-protocol-def
svmp-server