Route request timestamp

This PR relates to issue: https://github.com/jembi/openhim-core-js/issues/256.
No request timestamp was saved for individual route requests
This might not always work as the (new Date()) might be newer than the date set in line 61 (even if it is just out by a millisecond). Maybe you can store the time in a variable somewhere when setting it in setupContextForMulticast, then you can just check ctx.routes[0].request.timestamp against this rather than a new date?