Nodes snap to canvas grid

[orchetect]

• Add a grid size property to Patch, which defaults to disabled (free positioning of nodes)
• When grid is enabled:
  • Visually render grid as lines or points (optional)
  • Snap node positions to canvas grid when calling layout
  • Snap node positions to canvas when user drags node(s)

[wtholliday]

If the canvas is zoomable then zooming out on a big patch could result in too many grid lines to maintain a good frame rate.

could reduce the grid resolution in steps when zooming out.