Add eslint to normalize code style

[XatMassacrE]

Maybe it's not a problem for one person, but i think a uniform code style is important for collaborating.
So i add airbnb to normalize code, but i find warnings and errors are too much that i finally comment it.
But i reserve the basic config so you can custom your own code style.
By the way, webpack 2 replace loaders with rules, and i fix it.

[janhuenermann]

Thanks, this is great! Def need some kind of uniform code style, agree! But I don't have any experience with eslint or airbnb. Let me read about these tools first, before changing the code base/code style.

[andrewgremlich]

@janhuenermann you could definitely set the contribution criteria seeing as you started the repo.

Have you figured out eslint yet?