improving context loss support for WebGL
removing unused example
removed incorrect script tag in example 7; updated texture destroy in WebGLRenderer
Merge branch 'contextloss-fix' of https://github.com/mattdesl/pixi.js into culling

Conflicts:
	src/pixi/renderers/webgl/WebGLRenderGroup.js
	src/pixi/renderers/webgl/WebGLRenderer.js