Adds scripting MVP

[mgjm]

"Open an empty scripting demo"
MNScriptingDemo open.

"Open 'Alle meine Entchen' script"
MNScriptingDemo openAlleMeineEntchen.

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This closes #27.

[coveralls]

Pull Request Test Coverage Report for Build 158

• 0 of 90 (0.0%) changed or added relevant lines in 20 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.4%) to 54.028%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/MusicNotation-Core.package/MNMusicObjectWithChildren.class/instance/copyEmpty.st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNContext.class/instance/measure.st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNContext.class/instance/part.st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNContext.class/instance/project..st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNContext.class/instance/project.st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNNoteStatement.class/instance/context..st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNNoteStatement.class/instance/context.st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNNoteStatement.class/instance/note..st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNNoteStatement.class/instance/note.st	0	3	0.0%
packages/MusicNotation-Scripting.package/MNPitchBuilder.class/instance/context..st	0	3	0.0%

Totals
Change from base Build 156:	-1.4%
Covered Lines:	1757
Relevant Lines:	3252

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💛 - Coveralls