Add Pixi.JS library
Add canvg library

Note that it's added as a static copy. canvg is using SVN, so it can't
be added as a git submodule.
Add "pixi" and "canvg" to RequireJS config

Now modules can call:

  var PIXI  = require("pixi");
  var canvg = require("canvg");
Support Pixi.JS renderer in the base view (SVG container)
Implement simple atoms renderer that uses Pixi.JS
Use SVG template to render atoms (canvg), support canvas oversampling

However oversampling is disabled for now, as it obviously affects
performance.
Implement KE shading using Pixi.JS (quite demanding rendering mode)

It can be useful for benchmarks.
Fix PIXI atoms rendering (scale issues)
Implement mouse handlers for dragging atoms.

Both re-positioning when stopped and live-drag reimplemented.

[#57495382]
More-understandable names for svg container parts

A start on [#57495348]
rename MD2D "mainContainer" -> "atomsContainer"

[#57495348]

This clarifies its role.
Allow dragging the svg container's <div> not <svg>

[#57495348]

Since we'll split the single <svg> into several, we need to make sure dragging works.
Let renderers ask container to make a "viewport"

[#57495348]

Also, create 3 separate viewports in MD2D renderer
Fix an issue with gray outlines around the atoms

[#57495492]

It was also culprit of "too sharp" rendering.

It only happens when PIXI.Stage background is different from model
container background (and WebGL renderer is being used). Set both
backgrounds to the same value.
Set canvas oversampling to 1.5

[#57495492]
Restructure svg container into separate svgs

[#57495348]
Fix gray outlines around the atoms when background color uses rgba( )

[#57495492]
Implement rendering of atom labels using Pixi.js

[#57574886] [#57495848]
Merge branch 'master' into pixijs-rendering

Conflicts:
	src/lab/md2d/views/renderer.js
Fix gridline rendering in separate-rendering-layers

[#57495348]