Localization support

Localization support. Finnish language added as a second language for the system. Also fixed an issue that could have shown direct error messages to the end users.

Needs testing before merge

src/tjts5901/app.py

@@ -87,7 +87,7 @@ app = create_app()
 
 
 # a simple page that says hello
-@flask_app.route('/hello')
+@app.route('/hello')
 def hello():
     return _('Hello, World!')