Build System, Babel and ES6 src

* little filter-fix

* removed space

Dev vao state cache

* minimal texture bounds pass 1

* cheeky opts

* tidy up code

* create empty textures

* added empty texture

* couple more tweaks

* fixed empty texture issue

* fixed tweaked so id's sit on glTexture

means it should work on multiple contexts

* tweaked unbound textures

* tidy up

* upped max textures to 4 for mobile!

also sending state to tiling sprite VAO

* removed _activeTetureLocation

* tweaked eslint

* make sure buffer is bound

* updates based on @englercj review points

- Added vertexCount back in as it still yields much faster results in
iOS
- Tidied old comments
- Replaced i++ with ++i

Looks like since we call loseContext() on `WebGLRenderer#destroy()` that
if you create another WebGLRenderer with the same canvas the browser will
recycle that lost context and return it.

This means when we try to use the context it is actually in a lost state.
This change tries to restore a lost context before we use it. It also adds
a debug assert at one location that will be invalid if the context is
invalid.

cleanup some export defaults

* 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

* 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)

# 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