No error message is given if you leave MFI joining date blank

To Repro
=====

Click "create a center", enter in all required fields. Delete the default
date that is in the "MFI Joining date" boxes.

Actual
======
The user is kept on the "Create a center" page, but no error message is
displayed.

Expected
=======
Red error message should be diplayed at the top of the page (Please view other
pipelines to see error message UI):
Please enter the MFI joining date

This can wait until after v1.1-- esp since the date is defaulted until today's
date.

Emily