This PR changes the following:
* Landcover in z<12 is now less bright.
* Built-up landcover areas are now rendered more prominently in z<12.
* Unimportant roads are now white rather than gray.
* Water is now a brighter blue (thakns @kocio-pl).
* Low/midzoom roads are now rendered with bright halos.

This should improve the legibility and esthetics of the map. In particular:
* Roads, esp. primary roads, are now better legible on zooms 8-11
* Water areas are easier to recognize
* Minor roads on mid-zoom levels are rendered more clearly
* Residential areas are more prominent and easier to recognize