Collective.instancebehavior

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- No changes yet.

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- Invalidate global schema cache [jensens]

- Black code style, isort imports, overall housekeeping [jensens]

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- Be more explicit on dependencies and other egg improvements
[tomgross]

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- Fix ``DexterityInstanceBehaviorAssignable.enumerateBehaviors`` in order to
work with plone.dexterity >= 2.3.0
[agitator]

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- convert behaviors in ``enable_behaviors`` to tuple before concat.
[rnix]

- check whether instance behavior already in instance_behaviors before
adding.
[rnix]

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- created ``collective.instancebehavior`` based on jcbrand's and thet's work
[rnix]

- improved implementation with generic helper functions
[thet]

- problem description and initial implementation
[jcbrand]