Add initial support for XEP-0392

The last 3 commits added basic support.
Thanks @aaptel!

This commit adds basic settings interface to use it.
See `/color on|off`.

We still have to enable settings for color blindness.
And maybe another setting to decide whether to color the
occupantslist/roster with the same algo.

Regards https://github.com/profanity-im/profanity/issues/1191

src/ui/ui.h

@@ -317,6 +317,7 @@ void cons_room_cache_setting(void);
 void cons_inpblock_setting(void);
 void cons_statusbar_setting(void);
 void cons_winpos_setting(void);
+void cons_color_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);