Display a length scale on the map #46
Description
From openzim/zim-requests#1309 (comment)
Another is a scale, which would ideally just be some unit length, divided by effective current zoom amount (i am guessing zoom amounts are done logarithmincally, just guessing though). this should also be just changes to html/css, but this should ideally be visible at all times, somewhere on bottom side of screen (either left or right)