We should allow users to collapse and expand nodes (expose the metanode API via a GUI). This will be especially useful for dealing with set information from e.g. copurification experiments.

Note: IlianaAvila has implemented much of this in a Metanode plugin, but we need to pass this through group review and migrate this to a core feature and add additional functionality to the GUI to support multiple types of views on a metanode.  E.g. [[attachment:reactome_mockup]] (mockup via AllanKuchinsky and ImreVastrik)