Record notes in song editor

[achimmihca]

The song editor can re-use existing microphone and pitch detection features to record notes.
The recorded notes should go to a dedicated layer, such that the user can easily hide, modify, accept, or remove the recorded notes without any existing notes beeing affected.

This way, a user can use the recording feature in the editor for two things:
(a) record new notes to add to the song
(b) record notes to compare the recording with the current notes in the song to check if the current notes are correct.