Started with implementation of mocked tests

- it's not working right now, but have to commit to work later on
completed write of tests (from selfhost to mocked)
reorganized code

- removed unnecessary code
- renamed ITestHubClientEvents.cs to IClientContract.cs
- renamed ITestHub.cs to IServerContract.cs
- renamed ObservableHubProxyTests.cs to ObservableHubProxyFacts.cs
- renamed TypedHubProxyTests.cs to TypedHubProxyFacts.cs
refactored tests