Made some line-colors dependent on their polygon-fill

Objects with the following tags have now a border-color, that depends on
the polygons fill-color:

leisure=swimming_pool/playground/track/pitch
tourism=camp_site/caravan_site/picnic_site
landuse=field/retail
natural=field
power=station/generator/sub_station/substation
amenity=parking
aeroway=aerodrome

The dependency of both colors was expressed by adding:
line-color: saturate(darken(@color, x%), y%)
with 40 <= x <= 60
and 0 <= y <= 30
Added color-variables for buildings and made their line-color dependent on their polygon-fill

Affected tags:
* building=*
* aeroway=terminal
* railway=station
* amenity=place_of_worship
Merge branch 'line-color' of https://github.com/floscher/openstreetmap-carto into floscher-line-color

Conflicts:
	landcover.mss
Merge branch 'floscher-line-color'