Support touch devices

[melink14]

A lot of laptops now are convertable into tablets with touch interfaces and it would be good to support a way for touch users to easily look up words since hover model isn't so good there.

Ideas:

• Touch event
• Touch Gesture (swipe across word or something)
• Some UI element that the user drags around and which iniates a look up when near text

We'd also need to do something about the keyboard shortcuts for doing various things (we could add them to the box when in touch mode or have a toolbar or similar on the page.