Add Code for Local Matomo Instance

[cycomachead]

Here's the JS for sending visits to a local Matomo instance.

I also decided to add a cache buster for development mode in the service worker, which should help avoid caching issues when testing locally.

• Add a local matomo instance to snap.html + other demos
• Use a dev mode / local server cache buster in sw.js

[jmoenig]

thank you, Michael! Will pull for the next minor release, which, however, might take another couple of weeks. This is great, I love it!