code: @Exported
      public List<Plugin> getAvailables() {
          List<Plugin> r = new ArrayList<>();
          Data data = getData();
          if(data==null)     return Collections.emptyList();
          for (Plugin p : data.plugins.values()) {
              if(p.getInstalled()==null)
                  r.add(p);
          }
          return r;
      }
docs: Returns a list of plugins that should be shown in the "available" tab.
  These are "all plugins - installed plugins".