Use nav class for candidate lists

Makes them look nicer when hovered.
Allow choosing candidate list to show in locality page

By using the candidate list icons as navigation buttons that trigger
reloading the page with the 'mayor' or 'list' get parameters, and adding
a fake candidate list that is the list of mayor candidates.
Show candidate list in locality page when clicked

The default view is to show the mayorship candidates, but now when a
candidate list is clicked, its candidates will be shown instead. To go
to the page of the candidate list, click the title of the candidates
section in the locality page after clicking the candidate list icon in
the navigation bar.
To go back to view the mayorship candidates, click the yellow note which
is displayed above the candidate lists if a list is selected.
Highlight active list when selected

Color the ballot black because otherwise the "active" class colors it
white which is transparent over the white note image.