Add event markers to the calendar map

[seport]

As a user on the calendar page

I want to see pins on the map for all the events in the event list on the page.

When a user hovers on an event on the left side of the page, the corresponding pin should enlarge and/or change color to indicate that you're hovering on it.

If you're feeling adventurous you can add a basic tooltip on the pins with the event name, but we can put that off for another ticket if it's too much trouble.

Blocked by #37 #38

Notes:

This can probably be copied from the legacy code, but we might want to refactor it anyway. I'm pretty sure I wrote spaghetti code