Rework the open project dialog to contain only 1 dropdown

With the caveat that the qtQuickControls had to be updated to 2.3, due to a qt bug in 1.x that did
not update the dropdown popup list according to the ListModel.
This leads to a different look in the dropdowns and in the buttons of the open project dialog,
compaired to the rest of the application.

CURA-7609

plugins/3MFReader/UpdatableMachinesModel.py

@@ -0,0 +1,43 @@
+# Copyright (c) 2020 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+from typing import Dict, List
+
+from PyQt5.QtCore import Qt
+
+from UM.Qt.ListModel import ListModel
+from cura.Settings.GlobalStack import GlobalStack
+
+create_new_list_item = {
+    "id":   "new",
+    "name": "Create new",
+    "displayName": "Create new",
+    "type": "default_option"  # to make sure we are not mixing the "Create new" option with a printer with id "new"
+}  # type: Dict[str, str]
+
+
+class UpdatableMachinesModel(ListModel):
+    """Model that holds cura packages.
+
+    By setting the filter property the instances held by this model can be changed.
+    """
+
+    def __init__(self, parent = None) -> None:
+        super().__init__(parent)
+
+        self.addRoleName(Qt.UserRole + 1, "id")
+        self.addRoleName(Qt.UserRole + 2, "name")
+        self.addRoleName(Qt.UserRole + 3, "displayName")
+        self.addRoleName(Qt.UserRole + 4, "type")  # Either "default_option" or "machine"
+
+    def update(self, machines: List[GlobalStack]) -> None:
+        items = [create_new_list_item]  # type: List[Dict[str, str]]
+
+        for machine in sorted(machines, key = lambda printer: printer.name):
+            items.append({
+                "id":   machine.id,
+                "name": machine.name,
+                "displayName": "Update " + machine.name,
+                "type": "machine"
+            })
+        self.setItems(items)