Add text copy tracking

[i-like-robots]

This tracker listens for copy events on content pages and logs information about the selected text.

We do this because want to know how many subscribers appear to be copying above the threshold defined in our copyright policy and stop those that are offending. The Prospector project also aims to turn this potentially negative behaviour from B2C subs into an opportunity for B2B business.

To use it, import and initialise the tracker from this library, please note this should always be done behind the textCopyTracking flag:

import * as nTracking from '@financial-times/n-tracking';

if (flags.get('textCopyTracking')) {
    nTracking.trackers.textCopying();
}

This original implementation (from n-instrumentation, later n-ui) was intended to replace a third-party library for performance and privacy reasons.

More information about the FT's copyright program can be found here: https://docs.google.com/presentation/d/1WieqpEYvossMecte26tUPQK7CzWa-9SMGpyGQyzL738/edit?usp=sharing

cc #33

[i-like-robots]

I have also created a demo for the text excerpt generation: