Interactive font selector

[Simon Josefsson]

A feature request I have no idea how to implement:

Many word processors and text editors have a menu display on the
toolbar where you can select the font to display text in.  Text
editors usually use it simply change the font to display all text in,
whereas word processors use it to change the font of new text you will
write.

Both features seems useful in Emacs, depending on which mode you are
in.

(I use the term "font" here loosely, meaning slant, size, font
familly, color, etc.)