Add support for multiple URLs in an entry

* Fixes #398

The new Browser Integration entry settings page has a list view with any additional URL's. These URL's are added to the entry attributes with KP2A_URL_<counter>, which means those are directly compatible with Keepass2Android.

tests/gui/TestGuiBrowser.h

@@ -44,6 +44,7 @@ private slots:
     void cleanupTestCase();
 
     void testEntrySettings();
+    void testAdditionalURLs();
 
 private:
     void triggerAction(const QString& name);