App View: Re-ordering initialisation in App

LeapCursor should be initialised after Window because Window sets up
the current drawing context.
App View: Ensuring Paper resizes viewport on canvas resize.

Without this flag, the aspect ratio of Paper's viewport is messed up
by resizing the screen.
App View: BUG FIX: App requires a DOM element.

$(\#window) returns a jQuery object, whereas we need an
HTMLCanvasElement
App View: Changing add-subview to insert-children.

In keeping with the paperjs API.
App View: `select-at` sending paperjs doubleclick callback now

...instead of the `selected` method.

This allows for interoperability with mouse events, and additionally
means that standard paperjs Items can be used.
App View: Further Documentation

Documented the following:

 * app.ls
 * window.ls : Constructor
 * cursor.ls