Feature: sequencer.link_sequences_reviews as unique operator

Description of feature

Made sequencer.link_sequences_reviews as unique operator to fit Blender's operator design and allow python API for link_media_reviews.

Dropped link_single_reviews because this is not a common use case and can be managed through the UI. If the case raises, it'll be addressed.

Uniformized naming for clear_media_reviews.

Closes #322 (closed)

How to test it

Link or unlink media reviews

Checklist

Please check if your MR fulfills the following requirements:

• Unit tests have been added, if possible
• Documentation has been updated
• Build was run locally and any changes were pushed
• Lint has passed locally without error
• CHANGELOG.md has been updated

FYI: @awesome_dev_too