Embedding visualization is added to TensorBoard callback. (#5247)
Embedding visualization is added to TensorBoard callback. (#5247)

* Embedding visualization is added to TensorBoard callback.

* CI failure fix.

* Code review fixes

+ None or empty list for embeddings_layer_names implies monitoring
  of all layers of type Embedding
+ embeddings_metadata now can contain just a string with metadata
  filename if it's common for all the embedding layers.
+ Frequencies now takes 0-th epoch as first.

* Code review is in progress

keras-team/keras,keras-team/keras