code: function runCall(name, call, input) {
      return web.post(connectorsUrl + '/' + name + '/' + call, input);
  }
docs: executes a call on a connection.
  
  @param name of connection.
  @param call name.
  @param input data, i.e. an instance of a model or object compatible to the
  model in terms of attributes defined.
  @returns promise providing output/error.