On demand module exclusion for server mode

[grantat]

In a discussion with @anwala there is a desire to add the feature of excluding modules based on a request sent to the server's API. Since the last part of API URI is the URI-R, /cd/{URI-R}, there would be a need to a discussion about how to include the excluded modules in the API URI. We still want to be able to request URI-Rs with parameters as indicated in #15, ruling out the use of exclusions via query parameters. A few possibilities:

• Wayback style /cd{exclusions}/{URI-R}
• Custom routing/cd/e/{exclusions}/{URI-R}

[ibnesayeed]

This is a use case for a custom Prefer header. Also, the server needs to have a way to return the list of modules before client can decide which ones to use.