Use threaded image pull when adding new OMERO image
Looks like OMERO image is not fetched in the background when it is added as a new image.
To reproduce:
- Configure image source as OMERO
- Add new image to gel
Observe that there are no iocbio.gel.application.thread.thread_pool messages on starting/finishing; app hangs till image is added with the dialog display shown till the load is complete.