Path2D editor bug fix and improvement

- Fix #244 no path2d handles visible
- Update hotkey to be consistent with CollisionPolygon editor
- Add view-base point snap support (independent from node transform)

![](http://oi61.tinypic.com/2b713c.jpg)
Original curve

![](http://oi59.tinypic.com/xpzuia.jpg)
Use normal snapping, point is snapped to next step position

![](http://oi62.tinypic.com/28lz09w.jpg)
Activate view-base snapping, point is snapped to next grid point on view