wiab server overview diagram

[Dave]

I couldn't find an overview of the various bits of the wiab server, and 
how they plumb together. So from a couple of hours digging into the 
codebase, I knocked up the attached diagram.

I didn't include the Concurrency and Document/Conversation structure, as 
I suspect these are better visualised differently / separately.

Is there anything inaccurate or that should be added this diagram, and 
is it worth including in the wiki?


Dave