Add new banner fetch mechanism to the documentation

[Iankodj]

Include client-side mechanism to fetch the new banner from www.telerik.com.

The new banner is maintained remotely and it should be only injected (HTML+CSS). That is done thorough a proxy service:
https://docs.telerik.com/kendo-api/announcements/{product_name}

e.g., https://docs.telerik.com/kendo-api/announcements/kendo-ui.

Design: https://xd.adobe.com/view/a16fccf8-e58e-43aa-9fa7-0dcd656fd37b-f43c/

[Iankodj]

Details: https://github.com/telerik/docs-seed/wiki/Yellow-ribbon-banner-for-announcements#announcements-banner