Return access denied if user is blocked from accessing the webform

[jitendrapurohit]

Overview

Access Denied if user is blocked from accessing the webform.

Before

A hardcoded message is displayed if user is blocked on the webform. To test

• Create a webform.
• Enable Block unknown user from additional setting on civicrm tab.
• Access the webform as anonymous.
• A message is displayed on the top with few fields displayed too.

After

403 access denied is returned.

This also respects the access denied configuration on the webform.

So admins can enter their custom message, etc for the blocked users.

[KarinG]

Thank you @jitendrapurohit - test fail is being addressed in #936