Heightmap decal preview

From Linx on Discord:

WIP preview of a 'heightmap decal' terrain modifier. This will give us the ability to create points of interest using hand-placed terrain detail in a desired location at a higher quality than the planet's base height texture. It's not 'painting' detail in (it's more like slapping on a sticker!) but it could be used to create some interesting locations - the example here shows off the dynamics of the modifier