Support extended clock event specification
Need to support the new, extended clock event specification. Since it will take a while for front-ends to upgrade to the latest MOOC, we need be careful to maintain compatibility.
Clock events that don't have a clock type field can be passed on to the front-end. Old front-ends support this format and new front-ends recognize this form to mean "use whatever clock you have."
When a clock type is specified, and to maintain strict backward-compatibility, DPM may need to maintain a table of (front-end -> clock type) mappings so it would know whether a request can be sent to a front-end (in fact, this mapping may remove the need to update front-ends at all!) Discussion is encouraged.