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.
Let's move this function and `KeyboardRenderingManager`?

Also, instead of exposing the map itself, we should have the `UserTouchManager` getting the `key` (in place of `target`) at the very beginning of interactions.