custom error pages for 404 and 500 errors
i18n for error pages
minor: remove unused error pages
little bit of documentation
better detection if price link should be shown in the footer
Merge pull request #162 from azul/feature/3295-custom-error-pages

Feature/3295 custom error pages
Merge pull request #166 from elijh/feature/footer

better detection if price link should be shown in the footer
hash token with sha512 against timing attacs #3398