Make timestamp optional in firewall

Make timestamp optional in firewall - fixes buddylist issues introduced in https://github.com/uProxy/uproxy/pull/618.  This is a short term fix, long term fix to be done in https://github.com/uProxy/uproxy/issues/668

Tested in Chrome and grunt test (can't login to Firefox yet)
Why do you still have 'timestamp'?  Can you close this to reflect the actual expected schema in https://github.com/freedomjs/freedom/blob/master/interface/social.json#L42