[plt-scheme] Planned changes for PLT Scheme 4.0

Matthew,

Please take the two minutes it will take you to knock this proposal
out of contention:

> Someone ought to be able to show me how it's done these days, and put
> MrEd out of business.

Most of what GUI libraries provide is now available in Web programming
frameworks.  So:

Why not turn PLT Scheme entirely into a Web service, and the front-end
entirely into a Web application?  In the special case, the service
runs locally and the front-end communicates with the local back-end.
In the general case, you can run it across a network (having, for
instance, a big compute server running lots of jobs).

(There is still a serious research question here, which is how to port
the resource management work over to the Web context.  But that's
actually a research problem, not bone-sucking low-level engineering.)

Shriram