Change menu_headings to accept color and attribute

Instead of just accepting an attribute, it's now possible to
use a color, or both color and attribute, for example:

OPTIONS=menu_headings:inverse
OPTIONS=menu_headings:red
OPTIONS=menu_headings:red&underline

Default is still just inverse.
This lets the player change the menu heading color without
needing to use menu colors for them.

Also makes it so the core uses NO_COLOR instead of 0, for all
the menu lines which don't have any prefedefined color.

Tested for tty, curses, x11, qt, and win32

src/end.c

@@ -1081,11 +1081,12 @@ disclose(int how, boolean taken)
         if (c == 'y') {
             /* save and restore menu_headings in case something like
                #saveoptions is ever allowed to be run at the very end */
-            int save_menu_headings = iflags.menu_headings;
+            color_attr save_menu_headings = iflags.menu_headings;
 
             /* caller has already ID'd everything; we pass 'want_reply=True'
                to force display_pickinv() to avoid using WIN_INVENT */
-            iflags.menu_headings = ATR_NONE; /* don't highlight class hdrs */
+            iflags.menu_headings.attr = ATR_NONE; /* don't highlight class hdrs */
+            iflags.menu_headings.color = NO_COLOR;
             (void) display_inventory((char *) 0, TRUE);
             iflags.menu_headings = save_menu_headings;
             container_contents(gi.invent, TRUE, TRUE, FALSE);