Default set of headers added to all response objects.
By default the following headers are in this set:
Content-Type: text/plain; charset=utf-8
X-Frame-Options: SAMEORIGIN
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
If the Server header is added here and the serverHeader is set as
well then the value of serverHeader takes precedence.