When nodes are not resizable and grid is active, edges are painful to align #580
Description
When using snap-on-grid, node are placed on grid using top/left corner.
This applies for resizable and not-resizable nodes.
On not-resizable nodes, edge ends are most of time out-of-grid.
This lead to alignment issue and line glitches:
If not resizable nodes (border or nexus) where not anchored by the corner but by its center, edges would be on grid most of the time.
