Drop legacy online help system

Remove the old online help system and change the generic help key to do
the same thing as ":help".

This also removes some context-sensitive help. We should think about
re-adding support for this later.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.c

@@ -278,8 +278,7 @@ static inline void key_view_note(void)
 
 static inline void key_generic_help(void)
 {
-	wins_status_bar();
-	help_screen();
+	wins_launch_external(DOCDIR "/intro.txt", conf.pager);
 	wins_update(FLAG_ALL);
 }