Update ExceptionPage and fix the error title.

[jwoertink]

Purpose

Fixes #1920

Description

The ExceptionPage error messages used to say "Error 404", but they were changed to "Not Found". This updates the title to include both so now it'll say "Error 404 Not Found"

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test