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
fix #36746, link to handbook 2.0
remove unused stack-down action. Added here but never implemented http://sourceforge.net/p/mscore/code/4066/
change "AUTO" to "Automatic" in measure properties

and also capitalize the other entries in that popup
fix #36291: consolidate popup menus for line types

and fix capitalization
fix QComboBox items' capitalization in Debugger
fix QComboBox items' capitalization in Inspector
fix some more QComboBox items' capitalization

in UI files and
for note head names, where they get set programatically.
Also change Xcircle to XCircle.