[WIP] Use nwb for build, lodash babel, and es6 imports

[saminzadeh]

Took another stab. I believe we we're having issues with minification because we had a mix of commonJS and es6 imports. I went ahead and converted the code to be more modern JS (es6)

This diff accomplishes the following:

• Converts the codebase to use ES6 imports
• NWB for UMD, commonjs, and es6 build
• Jest for unit testing
• Lodash plugin to cherry pick the correct modules

You can try it on my own branch: https://cdn.rawgit.com/saminzadeh/itemsjs/es6-nwb-build/dist/itemsjs.js https://cdn.rawgit.com/saminzadeh/itemsjs/es6-nwb-build/dist/itemsjs.min.js

[saminzadeh]

Closing in favor of #22