Add new JS tracking heartbeat feature which replaces old one. New one is more...

Add new JS tracking heartbeat feature which replaces old one. New one is more performant and executes much less code on user websites.

New piwik.js tests included as well as an additional utility to make writing future tests easier (use jquery to parse tracker requests that are returned from fetchTrackedRequests). However tests don't currently pass since qunit is not super helpful for testing async code.