graphs and dependencies

hey @pablopareja we need to finish this. Take for example 

``` java
// inside GoTerm
public Optional<Stream<GoAnnotation<I, RV, RVT, RE, RET>>> goAnnotation_in() {

	return inManyOptional( graph().uniprotGoGraph().GoAnnotation() );
}
```

This is using the extension graph declared at `GoGraph`; but this should throw an exception if it is not present; and this exception should tell you about the graph that was missing. Also what you have in bio4j/bio4j-titan for building it should go here as abstract methods (I mean all the `withBlah` stuff)