Playhead: Show header line in the editors

[Gabrielxd195]

Currently the white line next to the playhead is only displayed in the song editor. however, the white line is not seen within the piano roll editors and the automation editor. I suggest you add the head line to have a better view of the playback head.

That way I would be inside the piano roll editor.

And so it would look inside the automation editor.

[qnebra]

Great UX improvement idea.

[Veratil]

I've added this in my PR for the Piano Roll #5253