Remove bower_components path from asset URLs

This is my proposition for the `bower_components` mess. Instead of only fixing that, I went further and removed `bower_components` from URLs completely, because to me they are kind of verbose and potential issues with name conflicts seem unlikely enough.

So instead of:

```html
<script src="../bower_components/modernizr/modernizr.js"></script>
```

we would have:

```html
<script src="modernizr/modernizr.js"></script>
```

Same goes for Sass. No more `../../../../` sillyness.

Fixes #150.