Remove hack in WelcomePagesModel and add WhatsNewPagesModel

CURA-6447

cura/UI/WhatsNewPagesModel.py

@@ -0,0 +1,22 @@
+# Copyright (c) 2019 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+from .WelcomePagesModel import WelcomePagesModel
+
+
+#
+# This Qt ListModel is more or less the same the WelcomePagesModel, except that this model is only for showing the
+# "what's new" page. This is also used in the "Help" menu to show the changes log.
+#
+class WhatsNewPagesModel(WelcomePagesModel):
+
+    def initialize(self) -> None:
+        self._pages = []
+        self._pages.append({"id": "whats_new",
+                            "page_url": self._getBuiltinWelcomePagePath("WhatsNewContent.qml"),
+                            "next_page_button_text": self._catalog.i18nc("@action:button", "Close"),
+                            })
+        self.setItems(self._pages)
+
+
+__all__ = ["WhatsNewPagesModel"]