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/console.c

@@ -1968,6 +1968,15 @@ cons_autoping_setting(void)
     }
 }
 
+void
+cons_color_setting(void)
+{
+    if (prefs_get_boolean(PREF_COLOR_NICK))
+        cons_show("Consistent color generation for nicks (/color)               : ON");
+    else
+        cons_show("Consistent color generation for nicks (/color)               : OFF");
+}
+
 void
 cons_show_connection_prefs(void)
 {