Grunt-preprocess, windows compatibility, changes to grunt pipeline

- `index.html` is now in `app/index.html`
- The `public`directory now gets copied 1:1 since it no longer holds `index.html`
- `index.html` is now shared between tests and app. I think some users were waiting for that for quite a bit. `grunt-preprocess` is responsible for picking the right parts.
-  The `build:dist` task is now just called `dist`. This makes sense because `build:debug` is useless by itself. Thus `build:dist` and `build:debug` are now just used internally and the `dist` dist task is now the public one.
- `grunt-preprocess` now replaces `dum-munger`. This fixes some issues on windows. https://github.com/stefanpenner/ember-app-kit/issues/247
- The development server is now even smarter. Copying of the public directory is no longer needed.
- Moved some grunt tasks around.
- Loom is now optional. Added install instructions and description in Gruntfile.js. https://github.com/stefanpenner/ember-app-kit/issues/247
- Fix: The development server didn't serve the test directory properly. https://github.com/stefanpenner/ember-app-kit/issues/251
- Everything now installs just fine on windows. This is necessary so that npm runs bower at the end.

This time I tested extensively. Everything should be fully operational.