Introducing OnTheSpot style of input methods

[Yokota K.]

Thank you for your comments, Riki and JMarc!

> That looks good, but of course, the devil is in the details. Note that you can create a new Row element type if this is useful.

Indeed, interaction between completion and preedit strings is a great concern. For the moment, I judged it would be ok since input method editor takes the control when preeedit strings are present, but there are various input method editors in various languages and systems, so it might be safer to create a new Row element.

Koji