Ghost cloud

Adapter model changes:
- Add *Cloud* of brokers instead of brokers being singletons.
- Replace *broker* with *connection* in adapters.  Connections are shared within threads.
- Minor performance improvements.  Got rid of a few unwanted queue declare().
- Add support for [queue] section in plugin descriptors.  When *false*, the agent will not declare request queues which are assumed to be managed elsewhere.

   ```
   [queue]
   declare = 0
   ```

- Documentation corrections.