Verifier must filter verification messages coming from firebase, knowing if the verification ID is on progress or not

[andrea-dintino]

The lack of a mechanism like above, produces a situation where the Verifier app keeps popping up the result of the same verification, potentially forever.

Solution:
1)
The Verifier generates a verification ID on request.
This newly created ID should be inserted in a list named "verificationIDsInProgress"
Upon finishing the verification (success or fail) the ID should be removed from the list

Upon receiving a message from Firebase, the Verifier should check if the ID is on the list:

• if on the list: proceed with verification
• if NOT on the list: discard

@puria please comment