it's now possible to define a custom menu without the need to copy all the menu entries from defaults.conf
if you want to define all the entries, disable the default menu with 'use_default_menu: False' under [main]
if a preheat is defined then defaults are dropped in favor of keeping only user defines, this behaviour
has not changed, and it's intended since the user may not want any of the defaults; but it's now possible to
put preheat options in an include file.
fixes#530fixes#497fixes#408
bc34b3c8d6