Move CatalogSearch layer override to event listener

Also removed unnecessary Fulltext resource override.
Implement better SPAM/firewall responses

Allows for blacklisted IP address to receive a verbose or sprase 403
HTTP response (added automatically by spam blocker and repeat hits).
Allows for admin added blacklisted IP addresses to receive an empty 404
or 503 HTTP response.

* Adds a Core App Model override to allow for event observers to have a
priority (so the blacklist can fail requests quicker).
Add a helper class to handler the logic for download reset visibility