Resolve "Calendar dialog for date of slot can only be exited by pressing "ESC""

Summary

When creating a slotted lab, a user has to pick a date for the lab using a calendar. Previously, there was no other way to close the calendar other than pressing ESC. Now, users can also just click outside of the calendar dialogue to close it.

Checklist

All items on this checklist should be checked.

• I have added a changelog entry.
• I have added tests for the functionality that I added.
• I adhere to the style guide.

How to review

1. Log in as somebody able to create slotted labs
2. Open a slotted lab creation page
3. Click on the date field and try to close the calendar by pressing ESC
4. Click again and try to close it by clicking outside the dialogue
5. Click again and see that clicking in the dialogue (but not on an actual date) does not close it
6. Click again and see that clicking on a day (that is in the future) chooses it and closes the calendar

Screenshots

Issues and tasks closed

Closes #751 (closed)