Streamlined css flow

Source maps seem to be mostly working for css. I'm not sure what the exact behavior is expected to be. `main.css` file is no longer created in `app` and is instead created directly in `dist`. I made the switch to `normalize-scss` and am importing that in `_base.scss` so we no longer have to copy over `bower_components`.

Fixes #56.

*This should be merged after #55.*

@pdehaan r?
Good catch.
This will theoretically work, but we'll need to create an "app/images/" folder into the repo and tweak the grunttasks/copy.js task to copy over the images/* folder. For example:
```
           src: [
+            'images/*.{gif,jpeg,jpg,png}',
             'index.html'
           ]
```