Beyond The End - Optimization and Fixes

Open a sloped hollow around BlockEnd's tower base

The towers are placed at a fixed height meant for the vanilla End. With
Nullscape's higher terrain the base and the elevator room end up below
the surface, so even with the interior carved the elevator sits at the
bottom of an end stone pit.

Before placing each tower, also remove the end stone above its base:
on the tower footprint (columns with a solid block in the two lowest
template layers) everything above the base, and around it with a slope
of one block of height per block of distance, up to 20 blocks away.
Only end stone is removed, so it looks like a hollow with natural
slopes instead of straight walls.