Show login page for non-logged in users that try to download netcdf file

Diana's prototype https://projects.invisionapp.com/share/4TX62TZDV27#/screens/417111554_Forecast_Download_login

To open the login from the product's view call to ModalLogin.open()

• Access to his method trough window.parent if you are inside the iframe
• If you need to call this method from another Plone view, call to ModalLogin.init() (example in product_view.pt)