remove RP2 config
Add support for surface-relative height
(<Setting name='Height' surfaceRelative='true' avg='1'/>) to clusters,
clouds and veins; add min/maxHeight settings to those distributions
for absolute height clamping; add min/maxSurfRelHeight settings to
substitute.
add Railcraft and TC4 support from Sandwitches
replace RandomLevelSource condition in standard configs with overworld
requirement, thus enabling support for ATG and similar