Add message bar to notebook tabs

[Mathias Brodala]

Every notebook tab in the playback area (playlist, queue, …) should have its own message area to notify about playback errors or the like. Other use cases are renaming of tabs either if the tab bar is hidden or always as well as prompts for saving.

If a message appears, the tab in question should also grab the focus to make sure users take notice.

[Mathias Brodala (mathbr)]

I don’t see this as necessary anymore. Playback errors are global and not bound to a specific playlist, renaming a playlist if it is the only one is a rare case and one can also set the tab bar to be always visible. And focus grabbing is bad, the maximum should be an indicator.