Add a View Cube to the viewport

[CiberNin]

Implement something like https://fennec-hub.github.io/ThreeOrbitControlsGizmo/ so that the camera can be rotated or snapped to an axis while a selection tool is in use.

[slimbuck]

done in #64

[CiberNin]

It looks like you implemented gizmos for orienting a splat in the scene, which is a useful feature, but my issue was about implementing a gizmo in the top right to control the camera so you can snap to front-back-left-right-top-bottom and corners.
Another example than the one linked would be fusion 360:

Being able to snap the camera to axis like this would make much easier to control point selections and align multiple splats.

[willeastcott]

Ah. So that gizmo is generally referred to as a 'View Cube'. I have changed the title of this issue and reopened it.

[slimbuck]

Done in #135.