Add RemoveAllEmptyStaves command

Add RemoveAllEmptyStaves command

Issue 4744

It has been noted several
times that we should have
a companion for RemoveEmptyStaves
and to also set remove-first to ##t.

A doc snippet, removing-the-first-empty-line.ly,
has become obsolete with these changes.

Contains commits:
Add missing word in changes.tely

Add changes entry for RemoveEmptyStavesAll

Use RemoveEmptyStavesAll for ossia example in
Notation Reference

This rewrites documentation for
RemoveEmptyStaves and adds
information on the newly added
RemoveEmptyStavesAll.

Add RemoveEmptyStavesAll command
Introduce a new context modification
identifier, RemoveEmptyStavesAll,
to complement RemoveEmptyStaves.

It sets both the remove-empty
and remove-first properties
of VerticalAxisGroup to ##t.