Fertilization for seed drills SoilMod Edition

This specialization adds under-root fertilisation to sowing machines.
Features V4 SoilMod-Edition (requires SoilMod v1.2.x !!):

separate fertilizer tank
enable/disable fertilization
change fertilizer type (A/B/C)
halfside shutoff for realistic creation of driving lines
separate use of ridge markers
Instructions included