Allow setting lookup font

[lynn]

Summary of changes

The Suggestions dialog allows setting a font for the text and strokes, but the Lookup dialog (which is powered by the same widget) doesn't have the same button. This PR adds that button:

(would it make sense to have an "always on top" setting here as well?)

Pull Request Checklist

• [ ] Changes have tests
• [x] News fragment added in news.d. See documentation for details