OMERO.matlab: write text annotation functions

See https://trac.openmicroscopy.org.uk/ome/ticket/10385

Given an image of identifier imageId, the comment annotation writing utility can be tested with
```
[c, session] = loadOmero(); % Assuming ice.config is properly configured
ca = writeCommentAnnotation(session, 'my-comment')
ca2 = writeCommentAnnotation(session, 'my-comment2', 'namespace', 'ns')
ca3 = writeCommentAnnotation(session, 'my-comment', 'description', 'my-description')
linkAnnotation(session, ca, 'image', imageId);
linkAnnotation(session, ca2, 'image', imageId);
linkAnnotation(session, ca2, 'image', imageId);
```

Similar snippets should be used to test `writeTagAnnotation` and `writeXmlAnnotation`.