[Reviewer: Andy] Fix 404 Not Found on Chronos timer notification due to / in call-id

Andy, I tracked issue 43 down to the same problem I initially saw when Sprout was failing to communicate with Ralf over the HTTP REST API due to "/" characters in the call-id. The fact that Perimeta almost always inserts a "/" in the call-id explains why I see the issue all the time, and you probably do not.