Use HTMLBars from published NPM package.

* Now actually publishing HTMLBars to NPM. We can let the HTMLBars build do all the work for getting ES6 output in the right place and ready to consume.
* Removes need to do crazy monkey patching/nesting inside HTMLBars.
* Enables us to use the specific version of simple-html-tokenizer for the version of HTMLBars we are using.
* Do not use `htmlbars-runtime` (ember-htmlbars is our runtime).