Fix initial camera rotation to be looking at center

[vincentfretin]

Fix initial camera rotation to be looking at center, same as in EditorControls when you start to rotate.

You don't see a difference in the inspector with the camera position at 0 1.6 2.
But with an initial camera position at 0 15 2 for example, you can see the camera jump when you start to rotate, that's because EditorControls rotate function forces the camera position to be on a sphere around the center that is at 0 1.6 0 defined at

aframe-inspector/src/lib/viewport.js

Line 110 in e2db22c

controls.center.set(0, 1.6, 0);