Adding a reference point for better orientation during panning

[nicolaisi]

When users perform panning with their right mouse click, the object is displaced and moved further away from its point of origin. It will be great to place a reference symbol at the origin to give users a hint of the origin's position.

You can enable the panning in the core.js file:
this._controls.noPan = false;

The right-click panning happens in the TrackballControls.js.