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.
ES6 will break [gaia-keyboard-demo](/timdream/gaia-keyboard-demo) :( ... please use ES5 before we have any better solutions.