Change frontmatter to be more standard

content/articles/2017/velikonocni-zavod.md

content/articles/2017/vhf-contest.md

content/articles/2017/vlastni-plugin-pro-netdata.md

content/articles/2018/a1-contest.md

content/articles/2018/krouzek-2018-2019.md

content/articles/2018/polni-den.md

...articles/2018/pozvanka-na-vyrocni-clenskou-schuzi-2017.md

content/articles/2018/vhf-contest.md

content/articles/2019/cq-ww-wpx-cw-contest-2019.md

...articles/2019/pozvanka-na-vyrocni-clenskou-schuzi-2018.md

content/articles/2019/vhf-contest-2019.md

content/articles/jak-nahlasit-chybu.md

content/articles/kontakt.md

content/articles/krouzek-mladeze.md

content/articles/o-radioklubu.md

content/articles/pro-cleny-rk.md

content/articles/test.md

content/articles/webkamera.md