Lore quest 1 Stealth: Use new elevations (#1953)

For this to work occlussion rendering needs to be disabled in the
"Stones" layer below the player and guards. Just as physics is disabled
for the same tilemap layer.

Also remove layer Stones Level 2 which had repeated tiles from Stones
Level 1.

Also remove Stones Cover layer. This fixes occluding the light from the
first guard.

Helps #1940
Fixes #1903
Fixes #1417

Author: manuq