OMERO.matlab: add a new function to update an original file

Given an existing `FileAnnotation` with an `OriginalFile`:
- add function to update the `OriginalFile` with the content of a local file
- update the `WriteData.m` example to illustrate this new functionality

NB: should the function be called against the `OriginalFile` itself or rather the FileAnnotation, e.g.

```
updateFileAnnotation(session, fa, newFilePath);
```

/cc @mporter-gre