Add missing preference back in

app/src/main/res/xml/preferences.xml

@@ -61,6 +61,13 @@
       android:key="@string/preference_colorize_nicknames_key"
       android:title="@string/preference_colorize_nicknames_title" />
 
+    <DropDownPreference
+      android:defaultValue="HIGHEST"
+      android:entries="@array/preference_show_prefix_entries"
+      android:entryValues="@array/preference_show_prefix_entryvalues"
+      android:key="@string/preference_show_prefix_key"
+      android:title="@string/preference_show_prefix_title" />
+
     <SwitchPreference
       android:defaultValue="false"
       android:key="@string/preference_nicks_on_new_line_key"