Bug-22: Add Word and WordStorage class

@john-hu Please help me review this patch. Thank you.
If we catch an exception, we need to provide a way to let UI know.
```
Bundle errorBundle = new Bundle();
errorBundle.putSerializable("url", urlToDownload);
errorBundle.putSerializable("exception", e);
mReceiver.send(INTERNAL_ERROR, errorBundle);
```