Contentful Codeblocks fixes

[kkartunov]

Scope to fix:

• indentation - breaks for copy/paste code into Contentful
• add line numbering
• make the theme look like on the marketing site

[kkartunov]

Look&feel like on blog https://www.topcoder.com/single-round-match-777-editorials/

[SathyaJayabal]

@kkartunov , do you have the url where these changes could be tested?

[kkartunov]

@SathyaJayabal when testing this one note:

• we decided to have different theme from the marketing site thus it looks different
  test here https://test-community-app.topcoder-dev.com/examples/contentful/viewport/f7JWRi9xxxsRQItjL1w6e

[SathyaJayabal]

Verified on test

• indentation
• line numbering

[sandhiyakavi]

Verified indentation and line numbering in Beta environment,working as expected.