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
proxy is there to be able to use two differents backend one for volatileStorage and one for persistentStorage.
But usually you don't need to use proxy, you can use redis directly or mysql or anything. proxy is there just if you want to mix two backend for the same storage.