add Piwik-Integration

[azine]

Hi,

here's a suggestion for a basic integration of piwik.

At the moment this version just checks if the piwik object is loaded and if it is, it tracks an event.

Most people will probably only either use piwik or GA, but if someone uses both, this solution also tracks the event in both systems.

What do you think? Worth merging?

Cheers,
d.

[devkinetic]

Rather than adding piwik to this plugin, you should instead fork this repo and create a videojs-piwik plugin.