Encode GIF in a worker that uses OMGGIF and NeuQuant.js

Worker version: http://forresto.github.io/mothereffinganimatedgif

Test colors fix:

before ![meag-599-before](https://f.cloud.github.com/assets/395307/497159/1a35e8be-bbf5-11e2-97fd-34c955e95f40.gif) 
after ![meag-599-after](https://f.cloud.github.com/assets/395307/497160/1d580040-bbf5-11e2-87f2-623765714c11.gif)

Test transparency:

before ![meag-trans-before](https://f.cloud.github.com/assets/395307/497166/36f480f0-bbf5-11e2-9aa8-de76531eaedc.gif) 
after ![meag-trans-after](https://f.cloud.github.com/assets/395307/497167/398af8a8-bbf5-11e2-8eda-74730c76c655.gif)

I took out the quality slider, because I don't think that it does much other than making NeuQuant spin for longer. If we want a quality setting we should figure out how to get NeuQuant to output 64 / 128 colors.

Transparency mattes to white and fills fully transparent pixels with #00FF00 green.

Tried to follow the conventions, but there were some structural changes to make it async. Instead of MFAnimatedGIF returning rawDataURL, dataURL, binaryURL, those get passed to the `done` callback.

Added progress % to the button while the worker is working.

Cheers all! Check out my [meemoo.org](http://meemoo.org/) project for this kind of fun with boxes and wires.

- Forrest