Fixes and minor enhancements for sub editor

- Zoom now works relative to the mouse's position rather than the center of the screen, much like Valve's Hammer Editor (or pulsegun's map editor shameless plug ;) )
- Rectangles now have line widths dependent on the camera zoom, not perfect but it's better than having lines disappear
- Fixed background resizing
- Fixed editor being completely broken because of no vsync, might still have a few bugs here and there
- Fixed selection rectangle not rendering at all when dragging from bottom right to top left
- Newline change in Item.cs

Subsurface/Source/Camera.cs

@@ -193,9 +193,13 @@ namespace Barotrauma
                     }
                 }
                  
-                moveCam = moveCam * deltaTime * 60.0f; 
+                moveCam = moveCam * deltaTime * 60.0f;
 
-                Zoom = MathHelper.Clamp(zoom + (PlayerInput.ScrollWheelSpeed / 1000.0f) * zoom, GameMain.DebugDraw ? 0.01f : 0.1f, 2.0f); 
+                Vector2 mouseInWorld = ScreenToWorld(PlayerInput.MousePosition);
+                Vector2 diffViewCenter;
+                diffViewCenter = ((mouseInWorld - Position) * Zoom);
+                Zoom = MathHelper.Clamp(zoom + (PlayerInput.ScrollWheelSpeed / 1000.0f) * zoom, GameMain.DebugDraw ? 0.01f : 0.1f, 2.0f);
+                Position = mouseInWorld - (diffViewCenter / Zoom);
             }
             else
             {