Adds ability to prevent login with unverified emails (#2175)

README.md

@@ -209,6 +209,11 @@ var server = ParseServer({
   ...otherOptions,
   // Enable email verification
   verifyUserEmails: true,
+
+  // set preventLoginWithUnverifiedEmail to false to allow user to login without verifying their email
+  // set preventLoginWithUnverifiedEmail to true to prevent user from login if their email is not verified
+  preventLoginWithUnverifiedEmail: false, // defaults to false
+
   // The public URL of your app.
   // This will appear in the link that is used to verify email addresses and reset passwords.
   // Set the mount path as it is in serverURL