Add a provision to make changes across multiple versions of the document

[andyi2it]

**Provision to add common changes across versions like banner **

Banners, popups, etc should usually appear across multiple live versions of the document.
Currently this requires deploying or updating old docs. This would make it more difficult as this new banner / other changes have to be updated in each version of the doc manually.

Proposing a new solution to update common things like banner, popup, etc across multiple documents.

Deploy a common js file in gh-pages repo
Add the common js file to docs

Any future common doc changes would only require changes in common.js