Added test showing group removal not working (esp with longpolling)
- Updated test project to not include private copy of CountDownRange
  and OrderedCountDownRange.

Conflicts:
	tests/Microsoft.AspNet.SignalR.FunctionalTests/Microsoft.AspNet.SignalR.FunctionalTests.csproj
	tests/Microsoft.AspNet.SignalR.FunctionalTests/Server/Hubs/HubFacts.cs
	tests/Microsoft.AspNet.SignalR.Tests/Microsoft.AspNet.SignalR.Tests.csproj
Fixed issues with group token.
- Make sure group token is properly updated on changes
- Made diffset just detect changes in groups.
- Serialize group token even if groups are empty.
- Added tests for the new diffset.

#2040
Call AddEventCore from SetEventTopic.
- This will stop overriden methods from running. DefaultSubscription
  was incorrectly calling AddEventTopic during SetEventTopic.

#2040
Make diffset work better.
- Truly Detect changes and added unit tests
  to verify new changes.

#2040
Fixed tests to use new JsonSerializer interface