Closing ISSUE-16

During the mailing list discussions, I feel like we reached some degree of
consensus that key expiration was something that would be left to
individual applications to implement, and not an inherent feature of the
API. Vijay captured a variety of situations where "removing" or "preventing
use of" (including raising JavaScript errors) would be the undesirable
behaviour.

Are there any objections to closing ISSUE-16 by:
- Removing startData/endDate from "first class" attributes on the object,
leaving them to be implemented within KeyAttributes instead
- Closing ISSUE-16