Building:
* Placing windows & lanterns next to stone columns is now less restrictive. This should also address not being able to place a window if there is a hidden column on the inside of the building ???????? * When a flat-roofed shape is fully inside another flat-roofed shape, the merlons are now correctly removed (just like they would be, if the shapes were only intersecting). This should make platform stacking easier and discovering it more intuitive ^^
* When erasing a wall, ivy is now more eagerly removed to prevent leftover bits left hanging mid-air
* Speaking of ivy, ivy is now properly removed from inside tall arches
