[packages] convert to ES6, add linting

[jchansen]

This PR converts all core lore packages to ES6 syntax and adds linting.

The primary reason for converting to ES6 syntax is to support tree-shaking, which requires generating a version of the transpiled code that leaves the import/export statements intact. This commonly results in packages being transpiled into multiple directory; a lib directory, contained the ES5 code (using require statements) and a es directory, where everything except the import/export statements are converted to ES5.

The es directory is then exposed as an entry point via the module field in the package.json file. Webpack 2 is configured to look for the module entry point before the main entry point, and will use that code if it exists.

This PR does not expose the module entry point because it makes for a breaking change in any ES5-style Lore projects.

The module entry point will be exposed as part of v0.13, along with making ES6/ESNext the primary syntax, and de-emphasizing ES5.