Use github-pages gem instead

Github provides this so we can use the exact same gems that they use
Remove JsonHelper and fix avsnitt.json

That plugin would not have worked on github, we would have had to
compile locally on our own.
Use a proper date_to_xmlschema filter so we get a date that angular can
understand.
Remove unused code in avsnitt.json
Add replace filter to remove " that would brake json
Use strip_newlines filter for content, otherwise json is broken