Feat / Creation of BackupCodeUsedEvent

[chaours]

Description
This PR let us have a BackupCodeUsed event dispatching.
We wanted to send a addFlash message to inform that the backup code is now obsolete and highly recommand to generate a new one right now.
I hope this PR will interest you.
Thanks

[chaours]

Hum... Many errors... I can try fix them.

[scheb]

There seems to be an issue with the unit test.

I also think, the implementation is a bit convoluted, as it introduces two extra dependencies into the CheckBackupCodeListener class, just to dispatch that event (the token at least could be taken from the passport object).

Though, TwoFactorAuthenticationEvents might not be the right event class for this. TwoFactorAuthenticationEvents was originally meant to represent the different phases of the 2fa process, so I think it's fair, if we'd introduce a dedicate event class for "checking codes". Could take the token (which contains information about the user) and the code as arguments.