Introduced a Manager to centralize plugin/package management

Should have done this from the start.
Will move other relevant scattered functions to this type.
For now it checks if the restart banner needs to show.
Taking into account that a user can toggle between enable
and disable without an actual restart. Even with multiple
plugins.

Contributes to: CURA-8587

plugins/Marketplace/Manager.py

@@ -0,0 +1,32 @@
+#  Copyright (c) 2021 Ultimaker B.V.
+#  Cura is released under the terms of the LGPLv3 or higher.
+from typing import Optional
+
+from PyQt5.QtCore import QObject, pyqtProperty, pyqtSignal
+
+from cura.CuraApplication import CuraApplication
+from UM.PluginRegistry import PluginRegistry
+
+class Manager(QObject):
+    def __init__(self, parent: Optional[QObject] = None):
+        super().__init__(parent = parent)
+        self._manager: "CuraPackageManager" = CuraApplication.getInstance().getPackageManager()
+        self._plugin_registry: PluginRegistry = CuraApplication.getInstance().getPluginRegistry()
+
+        self._manager.installedPackagesChanged.connect(self.checkIfRestartNeeded)
+        self._plugin_registry.hasPluginsEnabledOrDisabledChanged.connect(self.checkIfRestartNeeded)
+
+        self._restart_needed = False
+
+    def checkIfRestartNeeded(self):
+        if self._manager.hasPackagesToRemoveOrInstall or len(self._plugin_registry.getCurrentSessionActivationChangedPlugins()) > 0:
+            self._restart_needed = True
+        else:
+            self._restart_needed = False
+        self.showRestartNotificationChanged.emit()
+
+    showRestartNotificationChanged = pyqtSignal()
+
+    @pyqtProperty(bool, notify = showRestartNotificationChanged)
+    def showRestartNotification(self) -> bool:
+        return self._restart_needed