Customisable localisation of Feedback

[mazine]

1. Introduced Feedback.Message to store a message ID.
2. Added message field to an instance of Feedback, to localise messages on demand.
3. Covered all feedback cases with tests.
4. Moved message IDs to constants to simplify testing.
5. Not sure about new setters of Feedback class. I've updated them just to keep the API. But are the setter really required for this class? I can hardly imagine the use-case. Without them there is no need in the Feedback.Message class.

[vvatanabe]

5.　Not sure about new setters of Feedback class.
I've updated them just to keep the API.
But are the setter really required for this class?
I can hardly imagine the use-case.
Without them there is no need in the Feedback.Message class.

That's right. Setters of Feedback class does not need. So it is and I delete it.
And, thank you for me to fix the bug of "match.token".
Test is now very beautiful.
We're going to merge this PR.