Present target selection list directional arrow towards the selected target

[MrCsabaToth]

https://github.com/gdgfresno/DevfestARMap/tree/pointerarrow branch already should work (computing the direction between the world position of the target vs the world position of the scene camera - a.k.a the viewer - and turning the arrow towards that, but the arrow is misplaced in the AR scene.

Another approach to make the arrow's parent node the scene camera. In that case the arrow sticks to the viewer, but I'd like the arrow to be 0.5 m below the viewer and 0.5 m away towards the target as well.