Add yml validation schema generation and schema checker

[ClemensLinnhoff]

Reference to a related issue in the repository

#64

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• Automatically generate yml schema files by rules2yml.py. The schema files are generated in <rules_folder>/schema.
• Validate each rule file with the respective schema before loading it.

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@masipp, @jdsika

Check the checklist

• My code and comments follow the contributors guidelines of this project.
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation for osi-validation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests / travis ci pass locally with my changes.

[jdsika]

@ClemensLinnhoff we have some conflicts now

[ClemensLinnhoff]

@ClemensLinnhoff we have some conflicts now

I fixed the conflicts. Ready for review.