Cycle through grps, subs, libs, and dirs using left/right arrow keys

Nelgin's suggestion to support quick searching/scanning through message and file areas (e.g. comparing settings or whatever) without having to ESC then arrow key, ENTER, for each.

Uses Deuce's WIN_EXTKEYS UIFC mode flag, which I don't think I've used before now and uses the special -CIO_KEY value - 2 trick.

Also expanded the width of the sub-board and directory info windows to show more information (including full long name).

Fixes issue (wishlist item) #349 by Nelgin