Water flow logic tweaking:

- Less fluctuation, water doesn't constantly flow back and forth through gaps.
- Flowing water pushes characters around much more heavily, and the force is applied to the collider in addition to the limbs.
- Vertical gaps don't push characters up/down unless the character is roughly above/below the gap.

+ Renamed some fields in the hull and gap classes (Volume -> WaterVolume, FullVolume -> Volume, public fields start with a capital letter)

Barotrauma/BarotraumaShared/Source/Items/Item.cs

@@ -868,7 +868,7 @@ namespace Barotrauma
             if (CurrentHull != null)
             {
                 float floor = CurrentHull.Rect.Y - CurrentHull.Rect.Height;
-                float waterLevel = (floor + CurrentHull.Volume / CurrentHull.Rect.Width);
+                float waterLevel = floor + CurrentHull.WaterVolume / CurrentHull.Rect.Width;
 
                 //forceFactor is 1.0f if the item is completely submerged, 
                 //and goes to 0.0f as the item goes through the surface