so we convinced each other, kind of <g> Couldn't think of a use-case for "always hidden"
- basically, columns are for showing. If they for some reason aren't, then developers
are doing something fishy in the first place. Then they should cope themselves with it
in their unusual ways ...
The current implementation has two boolean properties: visible and hideable - the latter
forces the former into true if false. And yeah, the default column control dis/enables
the action in synch with the hideable thus supporting dynamic changes. If a developer
chooses to not add a visibility action, its her task to cope with dynamic changes. Don't
expect that to be too frequent, though.
Think we should leave it like this and wait for feedback.