Inject an ExecutionEngine in the groovy shell binding when generating reports.

Related to GitHub issue #8.
Empowers the programmer to use Cypher in the reports.
This will allow the report code to contain things like the below example.
```
import org.neo4j.cypher.javacompat.ExecutionResult;
ExecutionResult result = engine.execute( "start n=node(*) where n.name = 'my node' return n, n.name" );
...
```