Add line to COVID-19 alert banner

[saseestone]

We need to add a line to the existing COVID-19 alert banner letting users know that if they have returned materials to a bookdrop or via the mail, staff cannot process them. And therefore they will still be listed in Checkouts.

Perhaps:
"Library materials returned to a library bookdrop or by mail are being held for processing, and will remain in the Checkouts list until libraries reopen."

@jvine would love your eyes on the text before it deploys...

[jvine]

<br><br><b>Returned materials</b> <br>
Library materials returned to a library book drop or by mail are being held for processing. <br>They will remain in your Checkouts list until libraries reopen.