Terminal: Save settings on apply

Amends 3d354290be.

Change-Id: I467806afc27f1aef474f9058426b4c3119b53e8d
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/plugins/terminal/terminalsettingspage.cpp

@@ -434,7 +434,14 @@ public:
             });
     }
 
-    void apply() final {}
+    void apply() final
+    {
+        TerminalSettings &settings = TerminalSettings::instance();
+        if (settings.isDirty()) {
+            settings.apply();
+            settings.writeSettings(Core::ICore::settings());
+        }
+    }
 };
 
 // TerminalSettingsPage