Web fs image links

This is in develop as https://github.com/openmicroscopy/openmicroscopy/pull/672. In order to keep the UI code identical between FS and dev_4_4 branches, this branch should also be in dev_4_4, with the Blitz image.countFileSetFiles() and image.getFilesetFiles() returning nothing.

This PR shouldn't change the behaviour of the non-FS webclient.