Removed canvas tests
Removed a few others for elements that are not quite ready yet
Fixed the rest!

added a PREFER_WEBGL_2 to settings (false by default for now)

Using class names as ids for systems is bad! As uglify will me these
names up.

# Conflicts:
#	src/core/renderers/webgl/systems/MaskSystem.js
#	src/core/renderers/webgl/systems/RenderTextureSystem.js
#	src/core/renderers/webgl/systems/StencilSystem.js

Also created global uniformGroup
Broke up webGL to projection / renderTexture manager
I’m on to something here! Almost there..

# Conflicts:
#	src/core/Shader.js
#	src/core/renderers/webgl/WebGLRenderer.js
#	src/core/renderers/webgl/filters/Filter.js
#	src/core/renderers/webgl/managers/FilterManager.js
#	src/core/utils/index.js
#	src/interaction/InteractionManager.js
#	src/interaction/InteractionTrackingData.js
#	src/interaction/interactiveTarget.js
#	test/core/WebGLRenderer.js

* User can decide whether  auto-set the projection

`bindShader` always  set the projection matrix  automatically . in most case ,  that's OK.

But When I create some new renderer of PIXI ,  sometimes it would make some problems.
e.g.
* shader no projectionMatrix
* shader need use a custom projectionMatrix (not  _activeRenderTarget's)
* shader use a cached array (don't want to call toArray every time)

So I add a new argument to `bindShader` , and the default value is true, so  it would break any current code of PIXI

.

* Update WebGLRenderer.js

* Add a easy way to clear RenderTexture

In current PIXI, clear a RenderTexture is complex : 
```
renderer.bindRenderTexture(myRenderTexture);
renderer.clear();
// restore the previous renderTexture
renderer.bindRenderTexture();
```
And bind renderTexture is a high-cost operation . We shouldn't call it for cleaning render texture.

So I  add this method.

relatived : https://github.com/pixijs/pixi.js/issues/3595

* Add `return this`

* Added legacy option to webGL renderer

Setting ```legacy``` to true now forces VertexArrayObjects and
MultiTexture Batching to be disabled. We also store the variable on the
renderer just incase we want to use it to force settings in anything
else.

also added a test

* remove WebGLTests as they don't work on server

* Added extra param to Application

* Adds WebGL test for legacy

* Better check for WebGL in tests

# Conflicts:
#	src/core/renderers/webgl/managers/FilterManager.js
#	src/extras/cacheAsBitmap.js

Setting ```legacy``` to true now forces VertexArrayObjects and
MultiTexture Batching to be disabled. We also store the variable on the
renderer just incase we want to use it to force settings in anything
else.

also added a test