make donation popup less intrusive

even if we tried to reduce the level of nagging, random popups interfere too much with people's lives, as @elijah did note.

we've been talking about this, and with a new status window / splash screen it's way easier to think about less intrusive ways to ask for donations.

• one idea is to count (time, launches) and then display the donation popup inmediately after a successfull connect.
• instead of a popup, we could add some change to the systray icon (meaning "pending notification").
• the donate box can be added on the status window (with a close/dismiss button).