Create a new Message class to model a message that can be passed to an object living in another thread. Only an invalid message type is currently defined, more messages will be added in the future. The Thread class is extended with a messages queue, and the Object class with thread affinity. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>