Add layout for CFP page (using markdown)

Warning! Stylesheets are getting messy!

Use page.class to set body's CSS class,
then use crazy CSS selectors and duplicate them.
No SCSS nested blocks, sorry.
Add link to CFP in header

Remove link to speakers & talks at the same time
Tell about CFP "speakers" section of homepage
Improve CFP guidelines a little bit
Make CFP blog post shorter, link to CFP guidelines

Please note I had to change the already-published blog post!