Dialog was immediately being destroyed because a reference to it was not being stored in memory. Added a missingPackageDialog variable to WorkspaceDialog to fix this.

Swapped the loading order of Marketplace extensions so SyncOrchestractor is not fetched by PluginRegistry.getInstance().getPluginObject("Marketplace") in WorkspaceDialog.

CURA-8610

plugins/Marketplace/__init__.py

@@ -14,4 +14,4 @@ def register(app):
     """
     Register the plug-in object with Uranium.
     """
-    return { "extension": [Marketplace(), SyncOrchestrator(app)] }
+    return { "extension": [SyncOrchestrator(app), Marketplace()] }