Support multiple deployments of CSS

[oubiwann]

We use SASS to generate CSS. However, for dev and production, some of the resource URLs are different. We need to support multiple deployments:

• create a prod SASS wrapper
• create a dev SASS wrapper
• update the variables and other imported SASS files to use the deployment variables for image URLs, etc.

Part of epic #66

[oubiwann]

Done earlier today.