Rewriter of old to new settings format.

[wadoon]

This PR brings a tool for rewriting the settings in KeY files to the new JSON-like format. A requirement to get rid of the old property-based interface.

Changes along the road:

• The KeYLexer can be configured whether \proof is also treated as EOF or not. In normal mode, the lexer stops at \proof so that the s-expr of the proof are not going through the parser.

Plan

• Rewrite all KeY files

Type of pull request

• Refactoring (behaviour should not change or only minimally change)
• New feature (non-breaking change which adds functionality)

Ensuring quality

• Before overwriting the file, the reformater checks the parsebility.

[mattulbrich]

Agreed during meeting: Move to scripts directory. Reminder: When removing from the parser, make sure to give a descriptive error message.