Remove references to `window`.

These references are already setup properly using `this` which will work
even in non-browser environments or when we do not want to be working in
globals mode (for example when supplying `Ember.lookup` or
`Ember.exports` as mentioned in https://github.com/emberjs/ember.js/commit/305202f).
Generate independent module files.

This allows us to generate custom builds with specific modules embedded
without requiring the full package.

Specifically, this will allow us to generate an
`ember-template-compiler.js` without duplicating all of the details that
exist in `ember-metal/core`.
Merge pull request #4510 from rjackson/generate-independent-module-output

Generate independent module files.
Merge pull request #4509 from rjackson/remove-references-to-window

Remove references to `window`.