small adjustments to shadowing
- three-viewer now has basic support for post-processing:
 * initial/ very basic implementation for now
 * included relevant shaders/post processing source files from three.js
 * added attribute postProcess to web component, updated demos to apply it to one of the three viewers only (vignette effect)
 * a bit of related cleanup and restructuring (render() method, setupPostProcessing() method)
- small cleanup in undo/redo handling for three-editor
- removed object visuals changes (outline etc) from selection-helper
 * this allows users to define themselves what happens visually (or not) when hovering over / selecting an object
 * moved a cleaned up version of the visual effects to three-editor (again, because it makes sense to have these effects in an editor,
but not really in a simple viewer : seperation of concerns...)
fixed issue with hover/select not working with autorotating camera
- moved pointer move/ up/down event handling to the 3d viewer div itself:
 * fixes issues with event propagation: now clicking on html overlays does not select/deselect objects in 3d view
 * some related cleanups in most elements