Change the expiration behavior of sessionToken

See https://bugzilla.mozilla.org/show_bug.cgi?id=1022678

 - [x] Automatically prune ONE_DAY old not validated sessionToken
 - [x] cleanSession should remove both redis and longStorage keys.
 - [x] As soon as a sessionToken is validated store it in a long live storage
 - [x] Store the last usage and the date of activation of a sessionToken
 - [x] As soon as the persistentStorage is set prune volatile data.

We will use redis for the validation flow and as soon as the MSISDN is validated, drop validation data and build a longlive database entry to store MSISDN, creation date and last update date
> They are not using the same database even if they are using the same backend.

Yes. that's why we have two storages

```json
{
"storageA": {"engine": "redis", "database": "DATABASEA"},
"storageB": {"engine": "redis", "database": "DATABASEA"},
} 
```

You still did not explain why having a proxy configuration is helpful.

> This is useful to test cleanSession and cleanVolatileData behavior.

can you detail what you mean exactly by this ?