0.3.12 - Zoom improvements

• Center-of-mass and rotation handles should no longer sometimes be hidden beneath items.
• Handles scale size based on current zoom level, so tiny pieces are less likely to be hidden by them.
• Zooming now zooms toward the mouse. Due to the zoom smoothing, multiple zooms in quick succession may cause your target point to drift a bit as the cursor has not yet caught up with where it was previously pointing, but it's still better than it was.

Running into issues getting a good-looking outline that doesn't obscure more than it helps, that's now on the back burner, so highlighting on hover will remain for now.