OMERO.matlab: add function to retrieve thumbnails (see #10384) (rebased onto develop)



This is the same as gh-971 but rebased onto develop.

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Can be tested with

```
getThumbnail(session, image)
getThumbnail(session, image, x, y)
getThumbnailByLargestSide(session, image)
getThumbnailByLargestSide(session, image, size)
getThumbnailSet(session, imageIDs)
getThumbnailSet(session, imageIDs, x, y)
getThumbnailByLargestSideSet(session, imageIDs)
getThumbnailByLargestSideSet(session, imageIDs, size)
```