Adding highlight code and katex to initialisation

[steinerAdi]

Initial Situation

The sphinx extension does not enabling the code highlight script and the katex math parser.
To enable them, they must be manually enabled in the conf file of the users website.

New Features

With these changes, the user can enabling and set the path to the js file in the conf file without adding own js code or adding the script file and the initialization by him.
The new configuration variable are:

• highlight_code: False => Boolean to enable or disable the highlight code
• highlight_code_js: '' => Path string to manual link to the js file
• katex_math : False =>Boolean to enable or disable katex math parser
• katex_math_js: '' => Path string to manual link to the js file