Style of the initial bar line of a system.

In some engraving styles (mainly jazz), a double system initial bar line is used at structural articulations of the piece.

The PR supports this style, by adding a `_systemInitialBarLineStyle` variable to the `Measure` class which controls the style of the system bar line when the measure is the first of the system and by default it is set to NORMAL. This variable is not accessed directly; rather it is controlled by manipulating the system bar line. A system bar line can be edited:

- by dropping on it a bar line style from the palette (structural styles, like any repeat or END are ignored);
- by selecting it and double clicking a bar line style from the palette (same note as above).

It can be reset:

- by undo;
- by dropping on it (or selecting and double clicking) a NORMAL bar line style from the palette;
- by selecting and deleting it.

As the system bar line style is stored in the measure, if the first measure of a system changes (because of some other editing), the system bar line style will follow accordingly.
fix #39731: Stop midi flooding
Fix tab duplication when 'Apply' pushed in the MIDI import panel
Fix addition of imported MIDI files to the recent files list
Fix duplicate score name
Remove #ifdef because the 'if' branches become equal
Don't add recent score if it is already last in recent list
Fix empty recent file path: save file before add it to recent list
Fix last session MIDI file path
don't implode voices of different rhythms

as this it can lead to data loss.
On imploding staves it could lead to some incorrectness, but as the old
staves are still there, this can get spotted and fixed.
fix #40941: chord symbols don't transpose unless there are parts
fix #39851 - Crash on load of MusicXML file with pedal change but no start
fix several 'node not implemented' warnings
fix MusicXML export of overlapping ottavas (part of #30791)
fix MusicXML export of overlapping hairpins and trills (part of #30791)
update existing testfiles
fix #30791
remove spurious debug message
Merge pull request #1511 from MarcSabatella/40941-transpose-chords

fix #40941: chord symbols don't transpose unless there are parts
fix adding tempotext