Threedi-schema

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- Adapted versioning: prefix existing versions with 0.

- Fixed deprecation warnings of Geoalchemy2 0.13.0

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- Fixed packaging (also include migrations).

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- Fixed packaging.

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- Initial project structure created with cookiecutter and
https://github.com/nens/cookiecutter-python-template

- Ported code from threedi-modelchecker, rearranged into
'domain', 'application', 'infrastructure', 'migrations'.