Eventing Function definitions should have last modified timestamp

If we store a last modified timestamp in Eventing it would be useful for:

1) Determining the last change of an Evenitng Function in Nutshell for support tickets, further more if we kept a delta history of the last N (maybe 2-4 versions) if could be super useful for triaging issues due to an Eventing function change.

2) There seems to be some issues while editing a function where changes can be overridden prior to a save, e.g. you don't save your last changes due to a resync to the UI if we have a timestamp in the Eventing Function definition of last update we can ignore the resync in the UI (evenint.js) if the timestamp is the same as it was before we started editing. This I think is Fix #2 from  MB-36756 instead of a unique has we use a millisecond timestamp.