Fixed UniqueId timestamp problem, and added tests for DataManager & Added Derived Information Properties

- Added more tests covering Favorites & Recently Viewed in DataManagerTest
- Changed UniqueId to use a granularity of nanoseconds rather than seconds for generating UserContext-timestamp based UniqueIds.
- Changed IncrementalResult & Added an IdentityComparator, such that you can use the IdentityComparator to leave the items in the order they arrived in in the IncrementalResult, basically, a "null sort".
- Added ReplyCount derived information field to QuestionItem
- Added LocalDataManager implementation for ReplyCount & UpvoteCount derived information values.