Display call for funding somewhere within the UI

I think when we want our users to notice we need funding, we need to make it visible within the app, too.

I put a link to Liberpay into the about screen for the current 0.6.3 release, but I think we need to make it a bit more prominent.

The KDE has reported to have success with donation notifications:

• https://pointieststick.com/2024/12/02/i-think-the-donation-notification-works/
• https://pointieststick.com/2024/08/28/asking-for-donations-in-plasma/
• https://kde.org/community/donations/previousdonations/ (be sure to scroll down to the 2024 graph that shows a hockeystick graph with December 2024 donations peaking at > 100K)

We can try to learn something from their success. They are apparently employing a rather aggressive strategy by displaying a system notification:

Quoting from the second blog post above:

The idea here is to get the message that KDE really does need your financial help in front of more eyeballs — especially eyeballs not currently looking at KDE’s public-facing promotion efforts.

Now, I know that messages like this can be controversial! The change was carefully considered, and we tried our best to minimize the annoying-ness factor: It’s small and unobtrusive, and no matter what you do with it (click any button, close it, etc) it’ll go away until next year. It’s implemented as a KDE Daemon (KDED) module, which allows users and distributors to permanently disable it if they like. You can also disable just the popup on System Settings’ Notifications page, accessible from the configure button in the notification’s header.