Multiple imagesets on the Gallery picker plugin

It is currently not possible to restrict more than one nodetype on the Imagelink.

Reproduction path:

1. On the latest archetype, install the News module using Essentials.
2. On the CMS, navigate to the Document Types and then /hippo:namespaces/myhippoproject/
3. Edit the newsdocument document type
4. On the Image field, try to add more than one nodetype on the "nodetypes" property
   • Expected result: You can add more than one nodetype
   • Actual result: You can only add one nodetype