Use more sensible color scale for statistic data

[joergreichert]

most of the data have a certain value range that is far from zero, so it makes more sense to let the color range start at the minimum value instead of zero.

As alternative we might also use sensible value range classes with proper step ranges that fits the distribution as done here: https://codeforleipzig.github.io/opendata-leipzig-playground/11_leaflet_stadtteil_einwohner_torque.html and here: https://codeforleipzig.github.io/opendata-leipzig-playground/12_leaflet_stadtteil_einwohner_dichte.html