Add additional base scenarios

[CelticMinstrel]

I would like the scenario editor to offer more than one base scenario (the classic Blades of Exile Base). I'd like to have at least four bases to choose from:

• Surface base (white cave floor)
• Surface base (blue cave floor)
• Underground base (white cave floor)
• Underground base (blue cave floor)

The underground bases would differ from the surface bases in at least the following ways:

• The Warrior's Grove and default placeholder outdoors would be switched to cave floor instead of grass
• All town entrance terrains on grass would be replaced with town entrance terrains on cave floor. Possibly those currently on cave floor could be swapped to grass as well?
• Some other grass terrains may also be replaced by cave floor terrains.
• Holly and Wormgrass would become Toadstools and Crypt Shrooms, respectively.
• Possibly changes to some monsters and other items? Unsure.

[retropipes]

I would only support swapping cave/grass if this keeps the resulting terrain visually consistent. Likely the only way to know is trying in the editor. As for item/monster changes, items shouldn't change, as users would get confused. Monster swaps for those of equivalent stature expected in caves, on the other hand, I highly recommend.

[CelticMinstrel]

There certainly aren't very many items that should change; perhaps the alchemy ingredients are the only ones. As for monster swaps, the main problem is that I think most of the cave versions already exist in the default base, so I'm not sure if there's anything to actually swap.