Improve navigation for devices with just up/down/Enter

Improve navigation, so devices with just up/down/Enter keys can navigate menus.

Arrow keys now wrap around from the end of a column/row to the start of the next, and vice versa. Effectively, since fbwhiptail never actually presents an MxN grid, this means either up/down or left/right can be used to navigate any menu.

fbwhiptail's layout internals are cleaned up significantly. The nearly-unused "dynamic columns" mode was removed. The only case where this was used was a Yes/No prompt, which is equivalent to "dynamic rows" with exactly 2 columns (since Yes/No always has 2 buttons).

Signed-off-by: Jonathon Hall jonathon.hall@puri.sm