Add functionality for prefilling distribution from certain links (UTM tagging?) in the donation widget

[JorgenLjones]

Example use case: If a user reads about GiveDirectly on gieffektivt.no/givedirectly and they click to donate to them, they shouldn't have to specify GiveDirectly in the donation widget as well. At least 100% to GiveDirectly should be the prefilled default giving them the option to change the distribution if they so wish.