Fixed UniqueId timestamp problem, and added tests for DataManager

- 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".
Woa. We should keep hashcode comparisons, and we definitely do not want to allow duplicate items here.