Smk-python-sdk

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- Upgrade smk_api_common to 5.2.0

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- Bump smk_api_common to 5.1.0: reduction messages, cancel all feature
- Fix the broken flake8 build because of flake8-import-order

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- Update smk_api_common and eto_common versions

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- Removed obsolete smarkets.compatibility and smarkets.rest_api modules

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- Update smk_api_common version

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- 4.0.0 uploaded to PyPI is broken (it misses some files causing the package
to initiate a full piqi -> protobuf -> Python build process on installation),
4.1.0 fixes it
- Made most of the package's dependencies optional
- Improved Python 3 compatibility (all tests pass now), the package isn't
advertised as Python 3 compatible because there are some parts of it not
tested on Python 3 yet.