Added endpoint to restart the server with an API request

This PR relates to issue: https://github.com/jembi/openhim-core-js/issues/137
An restart endpoint is created that allows a request to be made to restart the servers
Can you rather make this a POST rather than a GET. GET requests should be able to be called multiple times without causing side effect whereas POST requests will cause some side effect. So I think restarting the server should rather use a POST just to make sure its not called by accident.