Moved the solution back to .NET 4.0.
Fixed unit tests.
Removed unneeded app.config file.
Fixed ExponentiallyDecayingSample by using nano-seconds ticks as in the Java verion, instead of either the Stopwatch ticks or datetime ticks.
Fixed the ExponentiallyDecayingSample; replaced the ConcurrentDictionary used before by a SortedDictionary, which is required to get the sample items ordered by keys, as required by the algorithm.
The value of Alpha required the time to be measured in Seconds, not Ticks or nanoseconds; that's now fixed.