code: function add (state, prefix, properties) {
    return Array.isArray(properties)
      ? addMany(state, properties, prefix)
      : addOne(state, properties, prefix)
  }
docs: adds one or multiple objects to local database
  
  @param  {String}          prefix       optional id prefix
  @param  {Object|Object[]} properties   Properties of one or
  multiple objects
  @return {Promise}