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
fix #40521: crash on adding text from within note entry mode
fix #40556: focus lost after duration change
enable plugin manager and creator unconditionally
fix #40581: overlapping ledger lines between voices
Merge pull request #1503 from MarcSabatella/40581-ledger-voice

fix #40581: overlapping ledger lines between voices
Merge pull request #1502 from Jojo-Schmitz/plugin-manager-creator

enable plugin manager and creator unconditionally
Merge pull request #1501 from MarcSabatella/40556-focus-duration

fix #40556: focus lost after duration change
Merge pull request #1500 from MarcSabatella/40521-text-note-entry

fix #40521: crash on adding text from within note entry mode
fix #29931: Custom key signatures do not show
fix #40016: Crash when closing score
fix #40686: handling of voice of explode/implode