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Add ``collective.taskqueue`` implementation.
[jensens]
- Refactor queuing code in order to allow additionla queue implementations.
This is a breaking change! All custom code importing from old ``taskzamqp.py`` needs adjustments.
The existing code and additional code goes under ``queue`` subdirectory.
[jensens]
- isort headers according to Plone rules.
[jensens]