Add water, sewage, and lava floor tiles

While the current water is great for outdoor scenes, it can't be used in rooms. A very simple way to provide indoor liquids is to add them as floor tiles, This allows creating aqueducts, sewers, and flooded areas in dungeons. These floor tiles don't have to be fancy, just easily distinguishable from normal floor tiles. Blue for water, green for sewage, red for lava.