Bug 1044525 - Use a WeakMap to hold layout key objects, mapped from DOM elements, to avoid poking with DOM elements in various modules aside from renderer.

- render.js's key properties normalization is now done in layout_manager.js, where it's more suitable to be in.
- Also, removed parseInt() on keycodes where suitable as we now retreive "number" from the objects held by WeakMap.
Yeah right, these should all go to `LayoutLoader`; if the `normalizeLayout` function end up too crazy maybe we need a `LayoutNormalizer` :P ?