code: function _createForceSimulation(width, height, gravity) {
      const frx = d3ForceX(width / 2).strength(CONST.FORCE_X);
      const fry = d3ForceY(height / 2).strength(CONST.FORCE_Y);
      const forceStrength = gravity;
  
      return d3ForceSimulation()
          .force("charge", d3ForceManyBody().strength(forceStrength))
          .force("x", frx)
          .force("y", fry);
  }
docs: Create d3 forceSimulation to be applied on the graph.<br/>
  {@link https://github.com/d3/d3-force#forceSimulation|d3-force#forceSimulation}<br/>
  {@link https://github.com/d3/d3-force#simulation_force|d3-force#simulation_force}<br/>
  Wtf is a force? {@link https://github.com/d3/d3-force#forces| here}
  @param  {number} width - the width of the container area of the graph.
  @param  {number} height - the height of the container area of the graph.
  @param  {number} gravity - the force strength applied to the graph.
  @returns {Object} returns the simulation instance to be consumed.
  @memberof Graph/helper