Update the single-page-tracking tutorial

[gka]

This page is talking about how to use Matomo in SPAs, but it's referring only to hashchange style navigation.

These days, SPAs are almost exclusively using pushState navigation, so it would make sense to update the documentation. The main points are:

1. Whenever your app is calling pushState or replaceState, you might want to call the trackPageView method
2. Then you probably want to listen to window.popstate events and send a trackPageView message as well

Most of the page can stay as it is, I would just replace the bits about hashchange with pushState.

[mattab]

Thank you for the suggestion @gka

Maybe it even makes sense for the page to explain both methods (not sure?)

[gka]

I guess it's ok to keep an hashchange example as reference for older apps.