Add fingerprintjs library

This collects a number of properties regarding the user's
browser and other system information and hashes them into
a semi-unique "fingerprint" that can be used to approximately
identify a browser.
Makefile: make vendor/fingerprintjs
Load fingerprintjs when not running in production environment
Submit browser "fingerprint" with each benchmark
Add information about privacy due to new fingerprinting

Alternatively we could have a checkbox to allow a user
to submit data without their fingerprint.