Openedx-filters

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Added
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* More significant arguments to the certificate creation filter.

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Added
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* Unenrollment filter definition.
* Certificate creation/rendering filters.
* Dashboard render filter definition.
* Course home/about render filters.
* Cohort change filter.

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Changed
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* Add fail_silently when importing filter steps.

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Changed
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* Fix dictionary mishandling in OpenEdxPublicFilter tooling.

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Changed
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* Use `run_filter` instead of `run` in OpenEdxPublicFilter tooling.

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Added
~~~~~

* Filter definitions for registration and login.
* Sensitive data mixin for filters.

Changed
~~~~~~~

* Pipeline runner from `run` to `run_filter`.
* Moved filters definitions to filters file inside their domain.