Add empty ListModel to store list of packages with

This model does nothing yet.

Contributes to issue CURA-8556.

plugins/Marketplace/PackageList.py

@@ -0,0 +1,22 @@
+# Copyright (c) 2021 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+from PyQt5.QtCore import Qt
+
+from UM.Qt.ListModel import ListModel
+
+class PackageList(ListModel):
+    """
+    Represents a list of packages to be displayed in the interface.
+
+    The list can be filtered (e.g. on package type, materials vs. plug-ins) and
+    paginated.
+    """
+
+    PackageIDRole = Qt.UserRole + 1
+    DisplayNameRole = Qt.UserRole + 2
+    # TODO: Add more roles here when we need to display more information about packages.
+
+    def _update(self) -> None:
+        # TODO: Get list of packages from Marketplace class.
+        pass