ui/ncurses: Change arrangement of boot order buttons

The buttons 'Add Device', 'Clear', and 'Clear & Boot Any' are short
enough to be positioned horizontally, but several localisations have
strings as long as all three buttons combined.

Instead arrange the buttons vertically and allow longer strings to
resize the width of the button to fit the whole string.

Signed-off-by: Samuel Mendoza-Jonas <sam.mj@au1.ibm.com>