kconfig/menuconfig: lxdialog is now built-in

lxdialog was previously called as an external program causing screen
to flicker when used. With this patch lxdialog is now built-in.
It is loosly based om previous work by:  Petr Baudis <pasky@ucw.cz>

Following is a list of changes:
o Moved build of dialog routings to kconfig Makefile
o menubox + checklist uses a new item list to hold all menu items
o in util.c implmented helper function to deal with item list
o menubox now uses parameters to save scroll state (avoids temp file)
o textbox now get text to be displayed as parameter and not a file
o make sure to properly delete subwin's before main windows
o killed unused files: lxdialog.c msgbox.c
o modified return value for ESC to match direct calling
o in a few places the code has been adjusted to 80 char wide
o in textbox a small refactoring was made to make code remotely readable
o in mconf removed all unused stuff (functions/variables)

Following is a list of know short comings:
a) pressing ESC twice will be interpreted as two ESC presses
b) resize does not work. menuconfig needs to be restarted to be adjusted

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>