Bug 1020847 - Add handwriting IME for Simplified Chinese.

Now, in this module, it's not only for creating canvas, but also for managing multi-canvas,  it's singleton, to some extend, it's a canvas manager. we have to think about the situation of multi-handwrting IMEs pre-installed.

When change it to a constructor,  every single handwriting layout associated with a HandwritingPadView object, we will have to manage the HandwritingPadView objects in IMERender.js.