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
You don't have to use the proxy, the proxy is there only when you want to mix two backends.