Add editable field to task in tasks tree API call [GIOT-44]

app/controllers/api/v20170715/core_api_controller.rb

@@ -20,6 +20,7 @@ module Api
               exp.my_modules.find_each do |tk|
                 task = tk.as_json(only: %i(name description archived))
                 task['task_id'] = tk.id.to_s
+                task['editable'] = can_edit_module(tk)
                 tasks << task
               end
               experiment['tasks'] = tasks