Include Server Performance in Browser Transaction

[nh758]

To get a complete view of a transaction's performance add the server metrics.

Update our response data to have data.performance and fold that server side performance into this current route set of measurements. Something like:

{
	data:{ data returned from server },
	performance: {
		jobID: "server side JobID",
		measurements: {
			key1 : { start: epochTime1, duration: measurement1 },
			key2 : { start: epochTime2, duration: measurement2 },
			...
			keyN : { start: epochTimeN, duration: measurementN }
		}
	}
}

Originally posted by @Hiro-Nakamura in #413 (comment)