Support a way to indicate an initial enrollment

[jessepeterson]

The webhook currently will inform you about TokenUpdate events. However they are explicitly meant to be sent multiple times during the lifetime of a device's enrollment. Thus, a TokenUpdate doesn't necessarily indicate an enrollment—unless it is the very first one. Support a way to track and signifiy an initial TokenUpdate in the event sent out so that enroll-time actions can be undertaken only once.

I imagine this would come in the form of a TokenUpdate counter that is reset every enrollment. In which case only the first TokenUpdate would represent the initial enrollment.