Encapsulate events JavaScript

[alancleary]

There's a small bit of JavaScript that has been used in both _includes/events-card.html and _layouts/events.html that dynamically updates the list of events so that upcoming and past events are organized correctly without having to rebuild the site.

In the starter site I added the events card to the events page as an example. This broke the page because the layout and card were trying to declare the same variables in this JavaScript. For this reason the script needs to be encapsulated in a common script.

[alancleary]

Done in commit 8a00615f77f5e3a7fd52ab2325ad791d5647cf0e.