ViewHelper: Simplified and prettified

[mrdoob]

Before	After

[ycw]

would be great if the axis color matches the translation/rotation/scaling gizmo :D

[puxiao]

This is a destructive update.

Where is my "XYZ" ?

I think custom configuration should be allowed.

em....

constructor( camera, domElement, labels=['X','Y','Z], spriteRadius=14 )

const viewHelper = new ViewHelper( camera, dom, ['右','上','前'], 20)