Test close connection
Implemented session layer as raw TCP client.

* NitroDebugger/GdbClient.cs:
* NitroDebugger/RSP/Presentation.cs:
* NitroDebugger/NitroDebugger.csproj:
  Refactoring to Presentation layer

* NitroDebugger.UnitTests/SessionTests.cs:
  Created test for Session layer (TCP socket)

* NitroDebugger/RSP/Session.cs:
  Implemented session layer as raw TCP client.