Remove "select all" and "select none" buttons for filters.

During user testing at the Digital Ready Maker Party, people un-checked
a box and expected that category to show on the map, which wasn't what
happened. Now we start out with nothing checked and show everything by
default; as soon as at least one box is checked, we show only the
checked categories.
if the window is big enough, show filters by default.
show category counts next to category names.