Feature: Display in-app notification indicator instead of push notification

[realpixelcode]

Depending on your in-app notification settings, Mastodon sends a push notification whenever someone favourites your toot, follows you etc.

While this makes sense when not using Mastodon, it isn't so helpful when Mastodon is opened. Instead, some kind of indicator symbol* should appear next to the notification tab's bell icon, just like in many other social media apps.

*How about a little blue dot?