[FEATURE] Optional inclusion of JavaScript

The inclusion of the piwik.js JavaScript file can be disabled by
setting the includeJavaScript option to 0.

This can be used for including multiple trackers in one page.
[FEATURE] Asynchronous tracking API

A new option useAsyncTrackingApi was introduced. If this is TRUE the
new asynchronous tracking API of Piwik will be used.

Resolves: #28216