This makes space in the Selection panel (at least on Windows; it
wasn't overfull on Unix) to add a new set of config options
controlling the mapping of UI actions to clipboards.
(A possible future advantage of having spare space in this new Words
panel is that there's room to add controls for context-sensitive
special-casing, e.g. I'd quite like ':' to be treated differently when
it appears as part of "http://".)