applets/notifications: improve paddings again

Reason for the change

Zero top padding is fine when there's only a summary label, but looks bad when there's body text, an icon, or both. Correct that.

Test plan

notify-send foo;
notify-send foo bar;
notify-send foo "bar is my second favorite variable name and this needs text long enough to become multi-line, but not scrollable";
notify-send foo --icon edit-bomb;
notify-send foo bar --icon edit-bomb;
notify-send foo "bar is my second favorite variable name and this needs text long enough to become multi-line, but not scrollable" --icon edit-bomb;
notify-send --app-name "Pompous Windbag" --icon face-yawn "Well actually" "It is very important that you listen to what I have to say because I am very smart and I know what I am talking about. When I say something, it is guaranteed to be illuminating and insightful, no matter the topic. That is why I talk so often: to help you gain the benefits of my great wisdom, so that you too may begin the process of achieving some fraction of my great knowledge. I know that this is useful to you, and that is the reason why I continue to speak at length on a variety of topics.";

Screenshots or screen recordings