Scenarios: Fix scenarios table list after delete action.

src/Model/Scenarios.py

@@ -60,6 +60,9 @@ class Scenarios(PamhyrModelDict):
         self.set(new._id, new)
         return new
 
+    def __len__(self):
+        return len(self.lst)
+
     @property
     def lst(self):
         return list(
@@ -70,8 +73,8 @@ class Scenarios(PamhyrModelDict):
         )
 
     def delete(self, key):
-        el = self._dict.get(key)
-        if el is None:
+        if key not in self._dict:
             return
 
-        el.set_as_deleted()
+        self._dict[key].set_as_deleted()
+        self._status.modified()