Image Annotation Extractor

This pull request adds an ImageAnnotationExtractor that extracts image annotations stored using the ImageAnnotator system on the Commons (https://commons.wikimedia.org/wiki/Help:Gadget-ImageAnnotator). 
Unfortunately not: Nodes don't have titles. After finding http://ochafik.com/blog/?p=393, I replaced that with a call to collect() in @9202afc. Is that more readable?

```scala
    val imageNoteStarts = pageNode.children.collect {                           
        case tn: TemplateNode if tn.title.decoded.equals("ImageNote") => tn     
    }
```