Fix #35136 : Tremolo bar always on top staff + crash on delete

A) A tremolo bar is always displayed on the top staff, regardless of the staff is it applied to

corrected by adding the ON_STAFF flag to a new `TremoloBar` object

B) Deleting a tremolo bar crashes the programme

corrected by adding the relevant case to the `Segment::remove()` method
fix #33391: view jumps when pasting in continuous view
fix #36621: display middle C as C4
fix #35176: ottava layout in various special situations
Merge pull request #1378 from MarcSabatella/36621-middle-c4

fix #36621: display middle C as C4
Merge pull request #1377 from MarcSabatella/33391-adjust-continuous

fix #33391: view jumps when pasting in continuous view
Merge pull request #1376 from MarcSabatella/35176-ottava-end

fix #35176: ottava layout in various special situations
Merge pull request #1374 from mgavioli/Fix_35136_tremolo_bar

Fix #35136 : Tremolo bar always on top staff + crash on delete