Show joined rooms, delete left rooms

To make the models update correctly in QML:
- ListModel and _QtModel merged
- Return a ListModelMap QObject from properties instead of
  a DefaultDict → QVariantMap

harmonyqml/backend/model/list_model_map.py

@@ -0,0 +1,36 @@
+from typing import Any, DefaultDict
+
+from PyQt5.QtCore import QObject, pyqtSlot
+
+from .list_model import ListModel
+
+
+class ListModelMap(QObject):
+    def __init__(self) -> None:
+        super().__init__()
+        self.dict: DefaultDict[Any, ListModel] = DefaultDict(ListModel)
+
+
+    @pyqtSlot(str, result="QVariant")
+    def get(self, key) -> ListModel:
+        return self.dict[key]
+
+
+    def __getitem__(self, key) -> ListModel:
+        return self.dict[key]
+
+
+    def __setitem__(self, key, value: ListModel) -> None:
+        self.dict[key] = value
+
+
+    def __detitem__(self, key) -> None:
+        del self.dict[key]
+
+
+    def __iter__(self):
+        return iter(self.dict)
+
+
+    def __len__(self) -> int:
+        return len(self.dict)