Persist year to URL

[ErikBoesen]

I think it would make sense to, for instance, set the URL to erikboesen.com/seniormap/2019 when the user selects 2019 as the year they want to view. I'm pretty sure there are ways to do this without reloading the page.

[AndrewLester]

Unfortunately github pages seems to do something odd with the URL that will just give back a 404 error whenever you go to a url like /seniormap/<number>. This would mean the year specific URLs can't be shared.

Instead, we can change the query string in the URL and work with that.