QoL: Add Map Icon for Stairs Down

Small change, good impact. Add the same icon for stairs up only flipped upside down and use it for entrances into burrows etc.

Right now all entrances / exits use the same icon, so this would help navigation in campaign areas such as Sceptre of God or the Ancient Pyramid. But it would also be a helpful icon to spot Starfall Craters or Abyssal Depths in maps.

Thoughts?

As someone who regularly goes back down the Scepter (I WILL DIE ON THIS HILL) of God, I approve this message.