Added plumbing for latency tracking

Essentially, we add a unique ID to each request. The client can capture this ID and report back when the page has rendered sufficiently. Then we can know a response time that includes client latency!

Based on idea at http://www.thumbtack.com/engineering/know-your-latency/
Merged origin/master
print statement? what print statement?
Added some blank lines.
Merge pull request #4 from Crossway/feature/latency-tracking

Added plumbing for latency tracking