Integrate with WPSEO_Options

[andizer]

Integrate with the WPSEO_Options framework and make sure option modification is done by using the get and set methods from WPSEO_Options

We should use the register_option (from: Yoast/wordpress-seo#13689) to register the option to the framework.

• Makes an options class that represents wpseo news specific options (must extend WPSEO_Option
• Register the option WPSEO_Options::register_option.
  • Rename version to news_version
• Retrieve values from the options by using WPSEO_Options::get
• Modify option values by WPSEO_Options::set
• Unittest as far as possible
• Check if Yoast/wordpress-seo#14082 is fixed by this

[maartenleenders]

LGTM, but there were quite a lot of changes so it's possible I missed something 🤔

[IreneStr]

Fixed in #591