Fix/player tag name handling

[Nianna]

Previously track names in track controller were the single source of truth, tags were removed on song load and (re)created on save.

In the new approach, P and DUETSINGERP tags are present in the tag list all the time. Track name update triggers multiplayer tags value update/creation. Tag update triggers track name update. On both song load and save the tags are not manipulated at all.
By default when track name is changed in track controller, the app:

• updates both DUETSINGERP and P tags (if already present)
• removes both DUETSINGERP and P tags (if present and the track name is cleared/set to default value)
• adds P tag if it is missing
  Using new property in settings, the default created tag can be changed back to DUETSINGERP (but only if txt format version specified by #VERSION tag is undefined, because since version 1.0.0 only P tags are allowed).

Minor fix - while track name was being edited, it was possible to choose "delete" option from this track's context menu, which resulted in exception in logs. Now context menu is disabled during edit.