Add preview functionality

As a marketing user I want to be able to preview how my storefront looks at a particular date.

Tech notes:

• Possibly need to have preview filter that sets current time thread local
• Evaluate all places where we use current time and refactor
• Need to think about security so that this feature is only allowed from a specific IP (Possibly through a Shop attribute)
• Need to inject some javascript that would enhance all links on the page + need some sort of indicator for what time is chosen
• This may not work inline with indexing as offline product could be removed from the index.