Huge refactor to match a new shiny eslint file.

Prefer const (#3002) ...

* added prefer-const rule to .eslintrc

* eslint const autofixes

* manual let to const changes; lint free;

* added brace style 'allman' to eslintrc

* brace style, comment fixes and default arg

* brace style fixes

* more brace styles

* Point default args

* Point brace styles

* Observable Point default args

* more brace styles

* jsdoc comment style

* brace style

* brace styles and small jsdoc fix

* brace styles

* removed unneeded eslint inline comment

* brace styles; lint free

small fixes in the documentation

filter pad fix

some more es6 changes (#2969) ...

* some more es6 changes
- const instead of let if possible
- arrow functions
- string templates
- argument defaults

* object property shorthand

* some more es6 changes
- const instead of let if possible
- arrow functions
- string templates
- argument defaults

* Revert "Merge branch 'dev-es6-sb' of github.com:stbaer/pixi.js into dev-es6-sb"

This reverts commit 8d3af81, reversing
changes made to e8b9948.

* Revert "Merge branch 'dev-es6' into dev-es6-sb"

This reverts commit 3eeaf79, reversing
changes made to fb69536.

* Revert "Revert "Merge branch 'dev-es6-sb' of github.com:stbaer/pixi.js into dev-es6-sb""

This reverts commit c860228.

* fix RenderTexture, incomplete merge

* fix for text font properties

* reverted some changes

* checked out License, Readme and Contributinf from dev-es6

* editorconfig updated: 2 spaces for .eslintrc

* added eslint rule: spaces around fat arrow

* used eslint fix for consistent spaces around fat arrow

* don't allow scale.x or scale.y to be 0 in displayObject setTransform

* removed jshint comments (again)

Fixes lint error

Merge remote-tracking branch 'origin/dev-es6' into dev-es6

Merged with 'dev' ...

# Conflicts:
#	src/core/Shader.js
#	src/core/graphics/Graphics.js
#	src/core/math/shapes/Rectangle.js
#	src/core/renderers/webgl/managers/FilterManager.js
#	src/core/sprites/webgl/generateMultiTextureShader.js

removed old jshint comments; replaced jshint in CONTRIBUTING.md with eslint

typo

fixed filter issue

fix filter offset issue

Replaces jshint with eslint, using babel in loose mode

Update imports and exports, getters and setters

Disallow the use of `var`

Implementing classes using the new ES6 syntax (#2936) ...

* Migration to ES6 classes

* Migration to ES6 classes

* Migration to ES6 classes

* Migration to ES6 classes

* Using babelify to transpile ES6 code

* Adding babel-preset-es2015 in devDependencies

fixed the jump blur effect

cleaning up WebGLState (#2826) ...

blendMode can be 2, so we have to set 32 to avoid problems

jsdocs rendertarget (#2819)

tweaked the filter manager to add padding AFTER clipping it to the renderer viewport ...

should fix weird blur filter effect when near edges of the renderer

added enabled to filters (#2798) ...

* added enabled to filters

* lint that code!

oops! missed a semicolon :)

fix that allows render targets to be passed to samplers ...

also allowed for resolution of texture to be specified when retrieving
from the filter texture cache

MaskManager - Sprite Mask Resolution (#2752) ...

Currently when applying a mask to a -x2 Sprite, the Sprite resolution is lowered to that of the mask.

fixed cacheAsBitmap filter issue

Dev bounds refactor (#2729) ...

* getBounds refactor

* another unit test

* added get local bounds

* local bounds stuff

* bound tests and tweaks

* added Ivans recursive function back in

* updated toLocal / toGlobal

* added toLocal and toGlobal tests

* linting

* tweaked tests

* fixed text bounds

added test for it too

* test tweak for text

* more tweaks to make it pass on server

* test tweak

Fixes jshint error in WebGLState

Merge pull request #2710 from englercj/doc-fixes ...

Multiple documentation fixes

Multiple documentation fixes

fastrect mask test (#2708)