add service func_key in user application
add func_key destination service  to func_key manager

needed to adapt extensions and func_key objects to deal with the fact
that foreign key of table func_key_dest_service is not service_id but
extension_id (all previous cases took for granted that table
func_key_dest_DESTINATION would have a foreign key DESTINATION_id)
add internal validation to avoid chaos and mayhem
add even more internal validation to avoid chaos and mayhem
restrict service function keys to be handled by new-style func-keys

only voicemail function keys are currently supported. All other service
function keys are still handled within phonefunckey.
add service func keys that don't need extra parameters