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)
I tried removing it completely but it was giving me different errors.  This is just a short term fix because uProxy is completely broken right now.  I'd rather just get this in today and work on other things for UX testing needed by Monday.  The alternative would be to completely remove the firewall until its fixed.  But we can do a more proper long term change in https://github.com/uProxy/uproxy/issues/668