Add validator for email address format

src/util/validators.js

@@ -59,3 +59,12 @@ export const bookingDatesRequired = (inValidStartDateMessage, inValidEndDateMess
       return VALID;
     }
   };
+
+// Source: http://www.regular-expressions.info/email.html
+// See the link above for an explanation of the tradeoffs.
+const EMAIL_RE = /^[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}$/i;
+
+export const emailFormatValid = message =>
+  value => {
+    return value && EMAIL_RE.test(value) ? VALID : message;
+  };