Openedx-filters

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Added
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* CourseRunAPIRenderStarted filter added which can be used to modify the courserun data for B2C dashboard rendering process.

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Added
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* CourseEnrollmentAPIRenderStarted filter added which can be used to modify the isStarted B2C dashboard rendering process.

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Added
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* InstructorDashboardRenderStarted filter added which can be used to modify the instructor dashboard rendering process.

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Added
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* CourseHomeUrlCreationStarted filter added which can be used to modify the course_home_url for externally hosted courses.

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Added
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* AccountSettingsRenderStarted filter added which can be used to modify the rendered output of the account settings page.

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Added
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* VerticalBlockRenderCompleted filter added which can be used to modify the rendered output of a VerticalBlock.

Changed
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* Introduced PreventChildBlockRender exception to the VerticalBlockChildRenderStarted filter.