Remove class diagrams.
More work towards fix.
Tentative fix for STOR-459

This fix replaces the old in memory surl status store (code hell) with a cache
implemented using the Guava cache library.

The new cache is smarter as it only maintains the status of requests that
could block other requests to ensure SRM integrity (i.e. put on file
pinned fails, get on file busy fails etc...)

The old cache could grow indefinitely in memory under heavy load, due to
terrible design of the database information lookup and of the status
comparison logic.