Update MauiKit's Nota

A few months ago I promised to test some KDE/MauiKit apps, sorry, I had a branch lying around with some updates but got lazy and forgot it over time. I'll try now to test those apps anew and check their data^^ But it'll probably take some time.

This is marked as draft since I'm unsure about the contents of the second commit:

• nota-git in the AUR seems pretty abandoned, shall it be included nonetheless?
• Since MauiKit seems to be developed by Nitrux, I've added their OpenCollective page. What is the policy on the donations field, are links to sponsor associate organizations allowed? Except GHex all the Donations links seem to be App- or Developer-specific.
• I've replaced the FreeDesktop categories with the ones from nota's .desktop file. Is that ok, and in general, should this field follow upstream metadata or should the categories be handpicked by this project (as described in Docs)?