Pykechain

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* :bug: Fixed a bug that was causing the part reference properties to not be copied correctly. (PROJ-241)
* :+1: Improved speed of the code by a different way of validation of the property options. We validated the property options using jsonschema validation on every instantiation of the property and that is overkill. Now we do it once we are updating the property itself. (1029)
* :+1: Added py.typed to the bdist package to indicate that pykechain supports typing. According to PEP-561.

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* :+1: Add additionally a `UsePropertyNameRepresentation` including additional testing for empty `config` objects inside the `Representation`. (KE-1239)

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* :star: We added filter `tags__contains` to `Context` (KE-1054)
* :+1: Added the `usePropertyName` property representation to sync with the possibilities in the backend. (KE-1239)
* :+1: dependent versions for development: requests (2.26.0), nbsphinx (0.8.7), coveralls (3.2.0), tox (3.24.3), sphinx (4.1.2), pre-commit (2.14.0), twine (3.4.2)

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* :star: We added the `Context` object to pykechain that has full API access to the `Context` API in KE-chain v2021.6 and newer. You can add time period contexts, static location contexts and textlabel contexta and put them under a `context_group` if desired. This `Context` feature is now implemented limitly for `Activities` but in the coming period will be extended to support extensive usecases for the Forms NG featureset that is coming this fall. (KE-925)
* :bug: Fixed a test cassette that was failing on a date check. Made it use a fixed date rather than doing it on today.
* :bug: Fixed automatic compilation of the pykechain documentation on https://readthedocs.org/projects/pykechain/.
* :+1: From now on python 3.5 is deprecated. The lowest version we support is Python 3.6. We can now start to insert f-strings and variable type annotations in our pykechain codebase.
* :+1: refactoring all models that were shadowed with a `<classname>2` to enable fast and smooth deprecation in July 2021.
* :+1: We converted all type annotations in comments to proper type and variable annotations.
* :+1: When connecting to a server with a SSL certificate error which cannot be checked, we provide a message fast and dont retry. (KE-1052, 997)

Backward Incompatible Changes

* We dropped support for Python versions 3.5 and lower. Python 3.5 reached end of life in Sep 2020 and no more new releases will be made. Consider upgrading to a newer version of Python. See: https://www.python.org/dev/peps/pep-0478/

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* :bug: Fixed an issue related to setting prefilters on a `ScopeReferenceProperty`.
* :bug: Fixed a bug related to a `UserReferenceProperty` not being copied over if there was a `User` already filled in. Improved the tests to cover all property types.
* :star: Added `CONTAINS_SET` filter type enum for `contains`.

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* :star: It is now possible to create, retrieve, edit and delete `ExpiringDownloads` using the `Client` and `Class` methods.
* :star: Added the GeoCoordinate representation for Geojson properties. We can now represent a geocoordinate as approximate address, Rijksdriehoekstelsel RD Amersfoort, as decimal degrees and degrees minutes seconds.
* :bug: Formatting of prefilters using lists in the `ScopeFilter` class is now based on comma's.
* :+1: Correctly formatted datetime strings are now accepted as valid datetime values.
* :+1: dependent versions for development: pytest (6.2.4), nbsphinx (0.8.5), coveralls (3.1.0), tox (3.23.1), flake8 (3.9.2), sphinx (4.0.2), pytest-cov (2.12.0), pre-commit (2.13.0), pydocstyle (6.1.1)