OMERO.matlab: add functions to read annotations (see #10385)

This PR addresses the first part of tasks listed in https://trac.openmicroscopy.org.uk/ome/ticket/10385 (annotation reading). 

Summary changes:
- refactoring of ``toJavaList``/``toMatlabList`` to support list of strings
- improvement of corresponding unit tests to have a more thorough testing of Java/Matlab types
- new ``getObjectAnnotations`` function wrapping ``loadSpecifiedAnnotationsLinkedTo``
- new shortcut functions to retrieve some image annotations (tags, comments, files)
- new ``getFileAnnotationContent`` function to download the content of a file annotation locally