show 'no definition found' message when no definition is found in dictionary lookup

so that users have a chance to query wikipedia or other online dictionary sources.

And this PR also adds a menu entry for E-ink screen full refresh rate which looks like this:
![screenshot from 2014-07-26 22 19 31](https://cloud.githubusercontent.com/assets/751535/3711331/ea350e84-14d0-11e4-881f-dec21a6b455a.png)

And holding on the "Custom" entries will give users the freedom to input any page number they want for a full refresh.