TTY: Add menu_overlay option

This was a request from a blind player.  It's hard to find
the left edge of the menu when it's drawn on the map, so
clear the screen and align menus to the left edge of the screen
when this option is turned off.

Originally this was called the window edge patch.

include/flag.h

@@ -199,6 +199,7 @@ struct instance_flags {
     boolean mention_walls;    /* give feedback when bumping walls */
     boolean menu_tab_sep;     /* Use tabs to separate option menu fields */
     boolean menu_head_objsym; /* Show obj symbol in menu headings */
+    boolean menu_overlay;     /* Draw menus over the map */
     boolean menu_requested;   /* Flag for overloaded use of 'm' prefix
                                * on some non-move commands */
     boolean renameallowed;    /* can change hero name during role selection */