[add] img tag (html) template in the post archetype; single page template for image display

See merge request cns-netadmin/cns-hp!91

[mod] read menu description in accordion from <Section>/_index.md

See merge request cns-netadmin/cns-hp!84

Resolve "javascriptの実装"

See merge request cns-netadmin/cns-hp!50

[mod] {{ partial 'header.html' }} -> {{ partial 'header' }} in baseof.html. this was the reason baseof.html couldn't write <meta> tag

Resolve "javascriptの実装"

See merge request cns-netadmin/cns-hp!49

[mod] css files, sidebar.html, to shape sidebar. [add] js on 'topic' class, to implement onclick behavior