Bug 1020847 - Add handwriting IME for Simplified Chinese.

Thank you for notice this before landing. This is pretty sad but we would probably accept this fact and land the patch first.

I think the proper fix of this would be rewriting `HandwritingPadsManager` into `HandwritingPadTargetHandler` and have it managed by `TargetHandlerManager`, so we would have one instance per pad. We will probably need to expose the user press object itself to all handlers so they will get x/y. Let me know what you think. We should file a follow-up bug for this.