Fix media queries issue for the index / add fullscreen capability

Add a new extension parameter: -baker-index-fullscreen

It forces the index view to use the size of the screen instead of the size needed by its content.
That way, you can use media queries for the index. Reference: [issue 637](https://github.com/Simbul/baker/issues/637).

You can also design an index that is not visually fullscreen (with a transparent background).

The index can be closed with a double-tap.