Add a configuration option "noreferrerLinks". When set to "true" the "HTML_NOREFERRER_LINKS" flag is being passed to Blackfriday. Thereby all *absolute* links will get a "noreferrer" value for their "rel" attribute.
See #4722
Add a configuration option "nofollowLinks". When set to "true" the "HTML_NOFOLLOW_LINKS" flag is being passed to Blackfriday. Thereby all *absolute* links will get a "nofollow" value for the "rel" attribute.
Fixes#4722