Misc warning fixes and related refactoring.

 - Added tests for export-rdf and graphml commands
 - Reindexing work into the GraphManager interface (which, relatedly,
  fixes need to do unsafe casts in the reindexer.)
Disable gunk logging
Graph manager refactoring.

 - The BlueprintsGraphManager now allows extension
 - The Neo4jGraphManager extends the Blueprints one and overrides
   methods where optimisations are possible.
 - Small changes to prevent (or suppress) warnings.