title: Change woocommerce error messages
body: <p>I would like to change the text of the error message that occurs on the checkout page when a customer hasn't filled in all the required fields. Currnetly, the message will display EVERY field that needs to be filled in, for example:
  "Billing address is a required field.
  Billing postal code is q required field.
  Email address is a required field.
  ..."</p>
  
  <p>I would like just ONE message that says "Please fill in the required field." or, if more than one field needs to be filled in "Please fill in the required fields."</p>
  
  <p>Does anyone know how to dy this? My PHP is limited.
  Thanks!</p>