[orca-list] Column headers are not brailled

["Justin Pospical" <jpospical fastmail com>]

Hi,

I can reproduce this one in both Orca's keybindings page and the Mate keyboard shortcuts dialog, and I'm 
unsure if this is the intended behavior. In the former case, when on a keybinding, pressing left and right 
arrow illicit the expected announcements of "command" and "keybinding", however these are not shown in 
braille along with the column. I have braille verbosity set to verbose.

Justin