[IMPROVEMENT] Remove arrows in visualzier or make them optional

[Thijss]

Based on feedback from the workshop session at the PGM meetup, I think it is a good idea to remove the arrows in the visualized grid or (at least) make them optional.

[jaapschoutenalliander]

In that case I would opt for making them optional (with a default = true to show them). Since the definition of from and to node do imply a direction it is not wrong to have the arrow I think.