allow nodes to add additional data to a stored message #131
Description
at the moment a message store has the functions
store() and change_message_state() suggestion is to add a method
add_additional_info_to_message() (TODO find a better name)
that allows consecutive nodes to store additional data related to a message in a message store.
if possible every node could have a param store which is by default False. If set to true the message (a JSON version of it) would be saved.