safeguard GUI against addPitch() returning 0
 #17906 (Using MIDI input to input chords causes crash): Reworked moveToNextInput() logic in addPitch(). moveToNextInput() is called before actually inserting a new node, except if adding to a chord or if it is the first note inserted. A new flag InputState::moveBeforeAdding has been added just for this purpuse.
fix #17906: when a chord is detected on MIDI input, the cursor is moved back before adding each subsequent note after the first, so that all of them become part of the same chord at the same position; the 'active' variable in MuseScore::midiNoteReceived() is used in a comparison, instead of directly as a parameter, since sometimes it can be -1
Fix #19374

Wide (two-digit) numbers in TAB collide; fixed
Separated Note::tabHeadWidth() and Note::tabHeadHeight() methods for TAB's from generic Note::headWidth() and Note::headHeight()
#16057: basic MusicXML export of chord diagrams
fix #15005
Corrected the typed commands in the Test section,
and added a similar Debug section.
Improved handling of mscore/revision.h

Add mscore/revision.h to .gitignore, since it is a generated file.
Remove mscore/revision.h from the git index.
In Makefile, add "revision" as a dependency of "debug", as it
already is of "release".
Merge pull request #153 from mgavioli/Fix_#19374_tab_numbers_collide

Fix #19374
Merge pull request #173 from softins/revision.h-fix

Improved handling of mscore/revision.h
Merge pull request #172 from softins/README-fix

Corrected the typed commands in the Test section,
Merge pull request #171 from lvinken/musicxml-fixes

Musicxml fixes
Merge pull request #166 from muelleki/17906-chords

#17906: Chord input from MIDI works again
Merge pull request #167 from watery/17906-midichordinput

fix #17906: chord MIDI input is fixed