The 404 Page uses the same "angry Jenkins" logo as the 5xx error page.

This can make it look at first glance that Jenkins is broken when it is infact (more likely) a user error, but it is also quite "intimidating" to see this.

The artwork logo used for a 404 should ideally be something more appropriate. (I would make a PR myself but it would look awful).

e.g. a Sherlock Jenkins (with a magnifying glass) or something.

Steps to reproduce

• start Jenkins
• go to $JENKINS_URL/job/this_does_not_exist/

Experience the angry devil Jenkins.

Notes

Just a case of a new image (the hard part!) then updating _404_simple.jelly and _404.jelly