Visualize vectorial quantities

[PythonFZ]

TODOs

• [ ] menu to select which quantity to visualize, e.g. forces / predicted forces
• [ ] fix issue with arrows not being displayed upon keypress but only on step
• [ ] menu should also allow multiple arrows with different colors (gather all available quantities from atoms)
• [ ] menu to select a multiplier for the force
• [ ] keypress vs. button?
• [ ] simulation box removes arrows