Grace period at the end of lab

At the end of a lab, the get next button should be shown for 15 more minutes.

This grace period was there previously, but is no longer working.

changed title from Grace period at the end of lea to Grace period at the end of lab

changed the description

added priohigh statusconfirmed typebug labels

This is problematic for us at CO since it blocks the TAs from gracefully handling the end of the lab.

mentioned in merge request !388 (merged)

created merge request !388 (merged) to address this issue

closed with merge request !388 (merged)

mentioned in commit f6256471