Update: Add 2.5 graphics for Smooth Ice Walls

Update for 50.08: Add new multi-tile fortification graphics for wood, stone and ice.

Update to sand and soil graphics to improve contrast, so walls dont appear to float above the floor.

Update fortifications with a new version.

Add Ice walls in 2.5d perspective.

Add fortification graphic
Fix missing graphic for standalone soil tile not being 2.5d