Inspired by this example by Matteo Abrate, I started a quest on my own. I added a snapping grid to fix dragged nodes with the help from mgraham. By double clicking a fixed node the force powers are applied again. Learned a bit about stopPropagation. Modifying the force layout  can be done with the buttons; add nodes by clicking the ‘plus’ button, and delete them with the ‘trash’ button. This answer helped me organize the code a lot! Add relations with the link button. The last button logs the nodes and links to the console.