Support Code Syntax Highlighting feature

[otarza]

As Readme of sparksuite/simplemde-markdown-editor says: in order to support syntax highlighting for different languages we need to add dependency to highlight.js and set codeSyntaxHighlighting to true under renderingConfig.

Tasks:

• Add highlight.js as a dependency.
• Add new Code syntax Highlighting option to text formats configurations, so admins will be able to enable this feature.