The session ids contain a Gorilla SecureCookie which internally encodes
"timestamp|value". As a result, newer session ids compare "greater"
than older ids. This is a problem for conferences where the participants
decide based on comparison of the session id who calls who, so later
participants always have to call all of the existing participants.
With this change, the (random) value is at the start of the session id,
resulting in "random" ordering of participants. Also some tests have
been added to check session en-/decoding.