TensorboardLogger defaults don't make sense

[constantinpape]

There are some issues with the TensorboardLogger default arguments. All log_X_every get the default argument None, which will be mapped to once every iteration. This is problematic:

• log_histograms_every set to once every iteration will lead to calling log_histogram and raise a NotImplementedError
• log_images_every set to once every iteration can result in huge log-files, because it stores a lot of images.

Probably the best solution is to change the handling of None for log_images and log_histogram

[constantinpape]

Thanks @ottogin for making me aware of this.