Fix: Basic schematic tests and `Schematic().to_sexpr()` structure

[mvnmgrx]

This PR implements:

• Testcase test_createEmptySchematic now finishes successfully
• Testcase test_hierarchicalSchematicWithAllPrimitives now finishes successfully
• Structure of Schematic().to_sexpr() was changed to fit these testcases (mostly changed where newlines were printed)
• unit token in class kiutils.items.schitems.SchematicSymbol is now optional
• uuid token in class kiutils.schematic.Schematic is now optional