Support CommonJS to be truly UMD module format, support npm

[tbenbrahim]

Add support for CommonJS modules, and npm, for tools such as webpack.

http://davidbcalhoun.com/2014/what-is-amd-commonjs-and-umd/

[tbenbrahim]

with changes, can be used from npm. Once pulled, npm install https://github.com/sandbochs/angular-dropzone --save, until then npm install https://github.com/tbenbrahim/angular-dropzone --save, although it might be more discoverable in the npm registry...