Emit metaDataChanged when changing properties

Properties is a dictionary inside the metadata dictionary. If you change one of the properties, it'll check afterwards if the dictionary is different from what it was before, but since the dictionary is passed by reference all the time, it'll think that the dictionary didn't change: The reference is still the same, so the thing it checks against is updated along.
This solution is a bit ugly but it does notice when the metadata changed inside the properties and then emits a change signal.

Contributes to issue CURA-2822.

cura/Settings/ContainerManager.py

@@ -218,6 +218,7 @@ class ContainerManager(QObject):
         entries = entry_name.split("/")
         entry_name = entries.pop()
 
+        sub_item_changed = False
         if entries:
             root_name = entries.pop(0)
             root = container.getMetaDataEntry(root_name)
@@ -226,12 +227,16 @@ class ContainerManager(QObject):
             for entry in entries:
                 item = item.get(entries.pop(0), { })
 
+            if item[entry_name] != entry_value:
+                sub_item_changed = True
             item[entry_name] = entry_value
 
             entry_name = root_name
             entry_value = root
 
         container.setMetaDataEntry(entry_name, entry_value)
+        if sub_item_changed: #If it was only a sub-item that has changed then the setMetaDataEntry won't correctly notice that something changed, and we must manually signal that the metadata changed.
+            container.metaDataChanged.emit(container)
 
         return True