Explore adding ability to dynamically update tracker configuration by calling newTracker with an existing tracker namespace

[fblundun]

The alternative is just to use existing methods like https://github.com/snowplow/snowplow-javascript-tracker/blob/feb8a3655ff75f1a9c09a9c9b500d0346340d82e/src/js/tracker.js#L1167

[fblundun]

See also #411