Resolve "Teacher can still see pick request button after request has been taken."

What does this mr do?

See #714 (closed) for detailed desc.

Actions taken to fix bug

• Conditional thymeleaf rendering

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• I adhere to the style guide.

Closes #714 (closed)