Move error page rules, other error page cleanup

Styles needed only by error pages are moved into their own stylesheets,
some stylesheets are renamed, and some old-design support is removed.
add source_url tracking for newsletter signups
Merge pull request #1865 from groovecoder/newsletter-signup-tracking

add source_url tracking for newsletter signups
Merge pull request #1817 from openjck/clean-up-error-pages

Move error page rules, other error page cleanup