[x] Make it so the url year reloads the page with just that year
[x] Make a separate year selector that gets used and changes the url year whilst all the polities are loading
[x] Make it so that even if that function is called and the page is refreshed (or just any time the page is refreshed) the loading of the shapes is not disrupted (might be impossible without using cache and the shapes are too much for that) - Edit not possible, so have added a warning note
Might be worth loading the GADM basemap shapes before all polities since it is faster anyway
[x] Update loading to say what it is loading, either all polities or specific year
Might be worth loading the GADM basemap shapes before all polities since it is faster anyway