Better hullbuilding process

[gallorob]

• replace original sloped blocks in spaceship with normal ones when adding hull
• keep only spaceships blocks set and work directly with that

[gallorob]

1337e1e replaces original sloped blocks in the spaceship with base blocks (keeping same orientations) when adding the hull.

This reduces the number of hull blocks removed because adjacent to sloped blocks on faces with no valid mountpoints.

[gallorob]

A more thorough analysis of which blocks to update yields significantly smoother slopes (452a0cb):

updated_hullbuilder.mp4

Will need to make it faster, or at the very least toggleable by users (simple mode: faster but more jagged edges; complex mode: slower but smooth and consistent slopes orientations).