kconfig: new configuration interface (nconfig)

This patch was inspired by the kernel projects page, where an ncurses
replacement for menuconfig was mentioned (by Sam Ravnborg).

Building on menuconfig, this patch implements a more modern look
interface using ncurses and ncurses' satellite libraries (menu, panel,
form). The implementation does not depend on lxdialog, which is
currently distributed with the kernel.

Signed-off-by: Nir Tzachar <nir.tzachar@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>