Create a clean master branch, add a grunt.js based build script and removed 'build' folder with gh-pages clone

FIxed #1042

I've removed the `build` folder with the gh-pages clone from the master branch and added a submodule to the original gh-pages branch for those who need the branch in their master. I've added a grunt.js based build script that compiles the LESS styles into CSS, minifies them and creates a font-awesome.zip file from all files in master. There is also a second target defined in the grunt.js buildfile. After checkout of the `gh-pages` submodule run

```
grunt pages
```
to compile the sourcefiles into the `gh-pages` submodule folder, which you then can commit to the original branch. 

This way Font Awesome can easily be integrated in automated build scripts and can be made ready for bower install without providing tons of unnecessary files.