Migration to ES6 and API providers in separate modules

[daffl]

This pull request migrates Feathers Core to ES6 using Babel and removed the API providers which are now in separate modules (#156).

Closes #156 and closes #183.

[ekryski]

Now that we are ES6 we should be able to remove lodash pretty easily.

[ekryski]

@daffl Nice work man. This makes the core so small. I ❤️ it so much!

I take back my comments about removing lodash. Pretty low priority because we are actually using it for some pretty legitimate stuff. Not just _.each.

[ekryski]

I guess once we roll this out we should update the examples in the database adapters to use the ES6 syntax or possibly add an ES6 example alongside the old ones.

[marshallswain]

Nice work! (like always:) So what's on the todo list before we merge this?

[daffl]

Documentation but I don't think that should block the merge. I started them in the https://github.com/feathersjs/feathers/tree/gh-pages-2.0 branch but didn't get that far. We need to do the reoganization we talked about, update all code samples to ES6 and add the topics that we'd like to cover and that are still missing.

Just for migration purposes we can just create a Gist that describes what is necessary (which should mostly just be replacing app.configure(feathers.rest()) etc. with var rest = require('feathers-rest'); app.configure(rest());).

[ekryski]

Yes, and also how you initialize the database adapters. Let's merge this PR and then we'll do a whole swath of documentation updates.