REEF c# does not write PID for Evaluators

Currently REEF .NET does not write PID files for Evaluators. This results in an thrown exception on Evaluator shutdown when using Local runtime with .NET Evaluators. It also leads to Job crash when shutting down C# local Evaluators for multi runtime.
The purpose for this JIRA is to have similar behavior across Java and .NET, By adding PIDStoreHandler that will be used in EvaluatorRuntime.cs to write the PID file.