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 #32651: Naturals should not be shown at system break
fix #7713
fix #35876
fix #39121, fix #20783
fix #40106
Automatic control of JACK/ALSA MIDI Out ports
remove duplicated file
fix warning reg. no return statement in function returning non-void
Merge pull request #1482 from Jojo-Schmitz/warnings

fix warning reg. no return statement in function returning non-void
Merge pull request #1171 from Igevorse/instrument-change

Automatic control of JACK/ALSA MIDI Out ports
fix #30976: No zoom with Ctrl+mouse
fix #40036: Tremolo through stem on grace note all eighths in 1.3 score
fix mtest
fix #40066: accidentals in chord symbols
Merge pull request #1483 from MarcSabatella/40066-german-chords

fix #40066: accidentals in chord symbols
fix #40031: stem tremolo on grace note. Also make tremolo size dependent of chord size.
fix #40216: Accidental on trill are not displayed anymore
album: don't add line break if page break
fix #40171: Crash in ~ScoreView() fixed