Poke module added for checking if server running

I wrote a trivial module that just returns `true` when requested. The point of this is that it can be used to  check if there exists a working connection between the Omnisharp server and the client.
I currently use it in the YCM client (https://github.com/Valloric/YouCompleteMe/pull/365) for checking if the server is running. It takes just one line and is platform independent :).