Implement a gizmo for reflection probe

Reflection probe gizmo should visualize the reflection probe box (including offset) without needing to set the debug mode on reflection probe. The gizmo needs to be inserted into the scene like selection boxes, so it should not cast reflections itself.

Reflection probes should also have an icon gizmo like lights and cameras, as it is normally invisible and thus cannot be easily selected from 3D view. hpaulaha should provide the icon. Same format/size should be used as existing gizmo icons (sample directional light icons attached).