Hmm, adding own categories is already supported in desktop app. The missing piece is, that in the mobile apps not all customized categories are supported. I still see the default categories in the mobile app, which I hided in the desktop app.
I agree. In my case I would like to have this feature for iOS as well. I can create my own categories and hide default categories in the desktop app. But in the iOS app I see again all categories. :-( The same for the Android app...