This completes some earlier work that did this change only in modularized code.

The last enabled EffectComposer pass is the only one that can really render to the screen, so we can set the renderToScreen flag in the passes automatically. The only case where EffectComposers don't render to the screen at all in the current examples is webgl_materials_skin, that sets up multiple EffectComposers and then combines their results. For that special case we now have a renderToScreen flag in EffectComposer.

This simplifies setting up EffectComposer and will make further enhancements a bit easier.

Now the same geometry and camera are shared between full-screen quad instances. A mesh is still created for each full-screen quad instance since that avoids repeatedly setting the material on the mesh in cases where a pass only needs one material.

The quad can be passed to renderer.render() directly without being a part of a scene.

This deduplicates a lot of code that used to be the same in a lot of postprocessing passes.

"Delta" is generally used to just mean change. The previous name didn't make it clear what was changing.

Also calculate deltaTime automatically in EffectComposer in case it's not provided.

Modified EffectComposer such that offscreen rendertarget size takes properly into account display pixel ratio

* add Pass.setSize() and have it called automatically by EffectComposer.setSize()

* fix minor bugs in EffectComposer.setSize routine.

* fix buggy prototype usage in Pass derived classes.

* fix buggy prototype usage in Pass derived classes.

* remove constructors as suggested by @mrdoob

* fix MaskPass's prototype.

* init pass side when added to compositor.

* tabify EffectComposer.js

* simplify for loop.

* Post-Processing: Introducing base class for Passes

* Post-Processing: move pass to effect composer

This reverts commit 644d6a21.

Conflicts:
	src/materials/Material.js

This commit enables three.js to manage the stencil buffer via material
properties.

should be `this.renderer`