[North Star Applicant UI] Implement client side validation for date question

[greg-hyde]

With date questions, we are using the memorable date component, which has 3 inputs instead of 1. On the server side, we're still parsing as a single input, so in order to clarify which input has an issue, we will probably have to rely on client side validation.

• Warn users when inputs are empty
• On blur, validate the date and highlight the issue, if possible (invalid day of month, improper leap year)