Decouple Canvas Functionality (v5) (#4429) ...

* Create canvas-renderer package

* Externalized all canvas-related functionality as packages

* Creates pixi-modern package (no canvas)
* Renames PIXI.WebGLRenderer to PIXI.Renderer
* Removes “WebGL” from class names, makes default

* Include modern build to Travis deploy

* Fixes linting issue

* Fixes app test on Travis

* Fixes Travis issues with app-loader mixin

* Add missing CanvasRenderer from accessibility tests

* More de-coupling, using _renderCanvas mixins, pixi.js inherits pixi-modern

* Re-adds missing dependency

* Re-adds other missing dependencies

* More strict comments elimination

* pixi-modern as a dependency is slow and bloated, undoing

* Fix ES global object

* Moves pixi.js to pixi.js-legacy

* Move pixi-modern to pixi.js

* Shared deprecations between bundles

* Adds unit tests for window

* Reorganized canvas and filter packages

* Renames renderWebGL functions to render

* Creates new canvas-display package for last of canvas functionality

# Conflicts:
#	bundles/pixi.js/src/index.js

* Removes preprocess, better deployment

* Removes deprecation packages, pixi.js-legacy now inherits pixi.js

Clear some properties in `ParticleBuffer.destroy()`. (#4407) ...

* Clear some properties in `destroy`

* Update ParticleShader.js

The ` vec2 v = aVertexPosition;` is needless , 
the  `v` is a new vec2 , use `aVertexPosition` will puzzle users (the people that read the code).

The  ` if (color.a == 0.0) discard;` will take unexpected result.

* Update ParticleBuffer.js

* cosmetic

Next Restructure for v5 (#4387) ...

* Reorganized files

* Adds new files

* Adds new files

* Updated to next-lerna

* Linting fixes, disable deprecations

* Created bundles and plugins folders

* Adds polyfill plugin

* Test pass

* Better build dest selection

* Externalized fragment shaders and vertex shaders

* Renamed plugins to packages

* Creates core package, updates Rollup version

* Reorganized pixi.js into packages

* Added packages, readmes, licenses for all packages

* Resolve minor build, dependency issues

* Ignore non-first comments with uglify

* Fixes fragment dependencies

* Adds settings, constants, utils, math, display, app

* Fixes import issues with core

* Fixes build all modules, updates deprecations

* Fixes listing issues

* Temporarily disable coverage

* Broke up tests

* Rename GeometryBuffer to Buffer

* Fixes tests for all

* Remove placeholder test

* Adds test for constants

* Add test for accessibility

* Created integrations tests

* Travis-friendly test concurrency

* Un-did concurrency for tests

* Better tester shebang

* Temporarily disable tests for mesh

* Log out floss error

* Moves filters to new filters root folder

* Combines premultiply, deprecates PIXI.extras namespace

* Documentation fixes

* Moves integration tests to tools

* TimeLimiter test is too unstable for slow environments