Add option to change shutdown/reboot keys (#487)

Include options in the configuration to change which function keys to use for shutdown and reboot.
Fix config.map_len size in src/config.c.
Add missing defaults in config_defaults() in src/config.c.

res/lang/it.ini

@@ -34,12 +34,12 @@ err_user_init = impossibile inizializzare utente
 err_user_uid = impossible impostare UID utente
 err_xsessions_dir = impossibile localizzare cartella sessioni
 err_xsessions_open = impossibile aprire cartella sessioni
-f1 = F1 arresto
-f2 = F2 riavvio
 login = username
 logout = scollegato
 numlock = numlock
 password = password
+restart = riavvio
 shell = shell
+shutdown = arresto
 wayland = wayland
 xinitrc = xinitrc