decrease `map_world` precision to 2x2km, to cut down data size

also: add missing tests for map_world and the csv view
restrict `map` threshold to 20, to make data size managable

this map is currently hidden, and not very useful. linked github issue
with ideas to improve it
add explanation on stats page, as to why the `unique` graphs aren't available
update cell/wifi locations as soon as there's any new data

note: the tasks inserting data are currently disabled on the live server
tweak the maps to show New Zealand in the initial state, fixes bugzilla 928189