menuconfig: Fix a case of visible symbols not being shown

Update menuconfig (and Kconfiglib, just to sync) to upstream revision
78682a8e3c4fe to get the following fix in, which could cause certain
visible symbols to not show up in the menuconfig interface:

    menuconfig: Always show implicit submenus with visible nodes

    Currently, the symbol BAR below (which ends up indented in an
    implicit submenu) is shown only if DEP is non-n (or if show-all mode
    is enabled):

      config FOO
            bool "foo" if DEP
            default y

      config BAR
            bool "bar" if FOO

    This is bad, because it hides visible symbols from the interface.
    The assumption was that an implicit submenu (which is only created
    if the parent has a prompt) would never have visible items when the
    parent item is invisible, but prompt-specific conditions and
    select/imply can break that assumption.

    Fix it by always showing implicit submenus with visible nodes, along
    with the parent node. If the parent node is invisible, show it in
    red, like in show-all mode (which happens automatically). That's
    probably better than having mysteriously indented nodes when the
    parent is invisible.

(Some other tweaks were made later to avoid showing red outside show-all
mode, because it might look confusing/broken.)

A new color scheme for the menuconfig has been added as well,
contributed by Mitja Horvat (pinkfluid). It can be enabled by setting
the environment variable MENUCONFIG_THEME to 'aquatic'.

The default theme has been tweaked to use bold text for the selected
item too.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>