To help lay out nodes more neatly, provide the option to snap to a grid drawn on the composition canvas.
- Render horizontal and vertical major grid lines on the canvas.
- major grid lines about 2 cm apart at default zoom level
- Add a menu item to enable/disable snapping to minor grid lines when placing nodes on the canvas.
- minor grid lines about 1/2 cm apart at default zoom level (vertical distance between ports on a node)
- only affects nodes placed after enabling snap-to-grid; does not rearrange existing composition
- Add a menu item to enable/disable rendering horizontal and vertical major grid lines on the canvas.