Propagate configuration and datastore errors

[rob-metalinkage]

If an underlying database issue arises during import there should be some way to propagate this to the administrator at least - via some logs perhaps - and configuration errors should be propagated to the end user.
A verbosity switch in the configuration may be the best way to deal with this.

This then becomes a key part of documentation for building a plug-in handler - what and how to propagate diagnostics for different verbosity levels.