MainWindow: Create a study file copy in current dire before update.

src/Model/Study.py

@@ -37,6 +37,8 @@ logger = logging.getLogger()
 
 
 class Study(SQLModel):
+    _version = "0.2.0"
+
     _sub_classes = [
         Scenario,
         River,
@@ -44,7 +46,6 @@ class Study(SQLModel):
 
     def __init__(self, filename=None, init_new=True):
         # Metadata
-        self._version = "0.2.0"
         self.creation_date = datetime.now()
         self.last_modification_date = datetime.now()
         self.last_save_date = datetime.now()