Move task helpers to own file.
[Resharper settings] Allow test names to have upper first char without warning
[PollingClient] Some guard clauses and tests
[IPersistStreams] Add batch size paramater to GetSince with extension method overloads defaulting to 100. Not yet used in implementations.
Rename IPersistStreams.GetSince to GetFrom.
Enable paging in GetSince in sql persistence engine.