Make "not available with old-style formatting" less obtrusive

[ulope]

The red "This operation is not available with old-style formatting." banners serve a very useful purpose but are rather obtrusive, esp. in areas where a lot of the examples are only new-style.

Maybe some kind of "widget" that shows the availability (possibly in a column beside the examples).

Something similar to (but hopefully less ugly :))

This will be even more needed once we add #24.