JNI: Remove obsolete msig_set_query_callback() stub.
JNI: Add Device.Signal.set_instance_event_callback().
JNI: Add Signal.set_callback().
JNI: Add several instances-related functions.

  - Device.Signal.start_new_instance
  - Device.Signal.release_instance
  - Device.Signal.num_active_instances
  - Device.Signal.num_reserved_instances
  - Device.Signal.active_instance_id
  - Device.Signal.set_instance_allocation_mode