Thumbnailbean

This PR addresses the issue described in https://trac.openmicroscopy.org.uk/ome/ticket/11072

The problem happens when 
 * The thumbnail service is recycled. 
 * The rendering settings are modified, which implies that the thumbnails must be created.
 * The thumbnail reloaded using the ```getThumbnail``` method for example.

To test, run
```./build.py -f components/tools/OmeroJava/build.xml test -DTEST=integration/ThumbnailStoreTest```


This PR will have to be rebased.