Adding ReplaySubject perf improvements

Closes issue https://rx.codeplex.com/workitem/35

Accompanying perf test console applications (https://github.com/LeeCampbell/RxPerfTests) shows performance is the same for Replay-By-Time and Replay-By-Time-and-Count.
However Replay-One, Replay-Many and Replay-All all benefit from the removal of the Scheduling and Time-stamped Queues. The removal of the extraneous code has the effect of less allocations being made for each subscription and OnNext call. This results in less Garbage Collections and a large increase in throughput.

The ReplaySubjectTests have been extended to ensure that while performance has been improved, that all existing functionality is maintained and remains consistent.