Implementation detail page: better Print CSS

[Deleplace]

Do print:

• a small header with logo
• the idiom statement
• the idiom picture
• the selected implementation
• the other implementations in the same language, if any
• the comments of the printed implementations
• A CC-BY-SA mention

Do not print:

• the username
• the favlang bar
• the languages links list
• all of the other implementations (even if in favorite language)
• the external links Demo, Origin, Doc
• the footer

[Deleplace]

This is what printing currently looks like