Add Review.version attribute

[eoyilmaz]

User Story

As a supervisor I want know which Version of a Task I'm reviewing so that when I approve the Task I now that I approved a certain Version along with the Task.

Acceptance Criteria

• Add a new column to Review class which holds the Version relation (Review.version and Review.version_id).
• Update Review.__init__() to accept a Version instance with the version argument.
• Add a _validate_version method:
  • Validates the Version instance.
  • Check if the Version.task is matching Review.task.
• Update Task class:
  • Update Task.request_review to accept a Version instance.
  • Add a new request_review method for the Version class that calls the Version.task.request_review() and attaches itself to the review.
• Add Alembic migration scripts:
  • Add the Reviews.version_id column.