Added example composer example with stitching, vignetting and bloom examples

Also included minified dat.gui library in examples/vendor dirs
Changed the bloom brightpass method
Change wording
Added sharpen filter to examples
Fix wrong viewport in Composer and gl.Clear(0) error

The viewport was correctly set on camera but then was erased by camera.setStateSet( element.filter.getStateSet() )
The correct behaviour is to set the viewport _after_ copying the filter's stateset.
Also setting clearMask at 0 leads to "Error: WebGL: Calling gl.clear(0) has no effect." on FF
Use the Composer.js from the source tree
Reuse the same quad geometry for all scenes

Also turn of backface culling
Fix mouse events on Chrome

I previously tried to manually place dat.gui but in the end it didn't worked well nor was required.
So we let it place itself automatically.
Also deleted no longer used css properties
Refactored the examples

Each effect is contained in a object which can create a composer and the corresponding gui.
Added chromatic aberration example
Split up each postprocess scene in a .js file
Added tonemapping example

Copied the .hdr decoding code from the hdr examples and reuse its textures
todo: compute avgLogLum from the scene
Improved tonemapping

We use the hardware mipmapping to downsample a luminance texture of the scene down to a 1x1 which approximate the average logarithmic luminance of the scene.
The tonemapping is also now done on the luminance part of the texel and not on the whole rgb colors (Yxy color space)
gitignore: *.thumbs.db .gitattributes: *.jpg/*.hdr binary

Windows automatically create a hidden file to handle image's thumbnails.
gitattributes not to diff (bigs) jpg et hdr.
Note: GitHub don't take into account (yet?) gitattributes so it will still show diff but only on the site.
Added more controls and fixes to tonemapping + new template

Added "locality" control to decide which mipmap level to fetch for the avg.
This enable local tonemapping.
Doing this, I discovered that the luminance scaling was actually wrong (denominator/numerator)
The scenes now load correctly on first selection, the mipmap generation was done before the scene had finished loading.
Added brightness, contrast and saturation controls (may contains bugs)
The sample now uses the template index.
Make a gui list to change current filter

Also changed the external vignetting radius default.
The folders are now open by default.
Added presets for tonemapping

Also a dat.gui fix -> https://github.com/dataarts/dat.gui/pull/46
Added the option to set user defined bounding sphere of a Lod, also added the related computeBound function
Fix middle bouton drag in examples templates on Firefox

Added display: block on the canvas
Btw, 3DView is an incorrect identifier, (start with a number), using a #3DView css selector on it didn't worked so I changed it by precaution
Describe and comment postprocess filters