Added support for IME composition

I added support for IME composition, which is needed to type East Asian characters. The issue was that zenpen recognised typing Japanese characters as selecting text and showed the toolbar. This patch fixes this issue.

Gif animations are attached below to illustrate how IME composition behaves.

**Original**
![before](https://f.cloud.github.com/assets/13040/1340372/690c6582-362d-11e3-9361-ee06c81ce9fd.gif)

**With my patch**
![after](https://f.cloud.github.com/assets/13040/1340373/6e831f24-362d-11e3-8fa8-9978c90277e8.gif)