Add support for empty ids input
Move object loading function to getImages() function

- Redirect getObjects() to getImages() if type is image
- Add support for empty identifiers using getUserImages() method
Allow toMatlabList() to convert ArrayList of Java objects
Add new tests for toMatlabList() utility function

- Test ArrayList of typical OMERO objects (Image, Datasets...)
- Test casting into a different class
Use toMatlabList() utility function and fix error when passing imageId