Fixes problem of not being able to add children with more than one level of hierarchy.

Editor: Moving delete shortcut handling outside of Viewport. Also showing Scene on top of scene graph.

I'm undecided about this change. Not sure if getObject* is better than getChild*.

Remove recursive calls from PolyhedronGeometry, replacing them with an
analytical construction of the geometry.

In unscientific studies, at high detail levels (> 5), this appears to yield
a ~30% reduction in runtime.

- from `THREE.BokehShader.generate(rings, samples);`
- to `material.defines = {RINGS: rings, SAMPLES}`
- thanks to @gyro3 suggestion in #3182

added break tags

updated documentation for constructor argument

added documentation for undocumented methods: add, addColor, addScalar, multiply, multiplyScalar, equals, lerp, getStyle, setStyle, setHSL, offsetHSL, getHSL.

removed documentation for methods that don't exist: getContextStyle, setContextStyle 

Removed reference to ColorUtils, which no longer exists.