Links should have href's in anchors

As depicted in #149 (closed), anchor tags <a> should have href attributes, so users can "right click + copy link" whenever they want. This MR also uses preventDefault and stopPropagation to stop the event from triggering an HTTP request, so we can use navigate like we'd expect in a SPA.

This MR also adds stopPropagation alongside preventDefault in Shpadoinkle.Html.Event.

Lastly, just as a stylistic inclusion, the 10px margin on the second "getting started" button has been removed, to provide consistency with the other button on the home page.

Before:

Compared to:

After: