Add subtype and node columns to job item
subtype column is a link to
ItemSubtype and should be used for easier filtering of the OTHER type jobs that are not linked to a plug-in.
node column is an text optional text column that can be used together with the
server column to further specify the computer that executes a job. For example, the server is typically set to the controller node in cluster (Open Grid cluster) and the node can then be set to the actual node that does the job.