Integrate grunt-dojo2 and redo distributions

[kitsonk]

In line with dojo/meta#18, this PR integrates grunt-dojo2 to rework the distribution format of packages.

root
└ dist
  └ umd - individual UMD modules with external sourcemaps which include inlined sources
    └ package.d.ts - The typings for the package
  └ esm - individual ES6+ targeted modules in es6 module format
  │      with external sourcemaps and sources (essentially for
  │      rebundling)
└ src - source TypeScript files
  package.json - CommonJS package meta-data
  bower.json - bower package meta-data
  typings.json - A configuration file for external typing dependencies
  README.md - Package's readme
  LICENSE - Package's license

The main in the package.json for this package points at /dist/umd/loader.js. This package also currently supports minification of the the loader.

Currently for grunt-dojo2 the commands dist and dist_esm are seperate (until we are confident that all packages build reasonably well) and the expectation is that the following will need to be run to build a complete distribution:

grunt dist dist_esm

• - I still need to add a prepublish script for this package, so it can be easily built.