Add option to only allow messages from jids in roster

`/silence on` will throw away all messages (type: chat, normal) that
come from jids that are not in the roster.

Implement https://github.com/profanity-im/profanity/issues/955

src/ui/ui.h

@@ -328,6 +328,7 @@ void cons_correction_setting(void);
 void cons_executable_setting(void);
 void cons_slashguard_setting(void);
 void cons_mam_setting(void);
+void cons_silence_setting(void);
 void cons_show_contact_online(PContact contact, Resource* resource, GDateTime* last_activity);
 void cons_show_contact_offline(PContact contact, char* resource, char* status);
 void cons_theme_properties(void);