Add download button to more pages + UI fixes

Signed-off-by: timoreo <contact@timoreo.fr>

launcher/ui/pages/instance/InstanceSettingsPage.h

@@ -81,6 +81,7 @@ private slots:
     void on_javaDetectBtn_clicked();
     void on_javaTestBtn_clicked();
     void on_javaBrowseBtn_clicked();
+    void on_javaDownloadBtn_clicked();
 
     void applySettings();
     void loadSettings();