Add a request id field in messages

[arkanoider]

Hi @grunch @bilthon ,

as requested from @bilthon as enhancement for clients I have added a very simple request_id in messages that will echo the received one from client messages. I understood that this thing is useful for clients so I want to refactor code with a more clear implementation.

Now I extract from incoming message the field and propagate it in all actions, but in some cases i put an option in the field, for example if there is a resubscribe action of an invoice at mostro startup i cannot add it because i did not receive a message from the client, the are some other cases like that, typically in invoices management. Now I ask you if we need this new field also in these case? @bilthon drop me your ideas of the messages where the echo is needed.

I have in mind two ways to improve this:

• Add an atomic static variable, so I can use it everywhere easily, but still usable no for all messages.
• Add a db field so we can still have this number available.

Drop me your ideas here...

[arkanoider]

Started implementation and almost closed via #376

[grunch]

closing it via #376