added option to initialize wandb outside logger

  def setup(self):

    """Initializes a W&B run and create a run object.

    If a pre-existing run is already initialized, use that instead.

    """

    if self._wandb.run is None:

      self.wandb_run = self._wandb.init(**self.wandb_init_params)

    else:

      self.wandb_run = self._wandb.run

    self.initialized = True

  def check_other_loggers(self, callbacks):