Documentation inconsistencies and mistakes - tools / embeddings / tsne, phate, umap

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1. The documentation of sc.tl.tsne and sc.external.tl.phate weren't updated to indicate that X_{tsne,phate} are obs*m* fields
2. The documentation of both sc.tl.tsne and sc.tl.umap don't indicate the addition of the uns dictionary with the details of the embedding parameters
3. The uns dictionaries returned by sc.tl.tsne and sc.tl.umap don't seem to follow the same logic: tsne's param dictionary holds most of the adjustable parameters (even irrelevant ones like n_jobs), while the umap dictionary holds only a and b parameters.

Start with the documentation and implementations for sc.tl.tsne, sc.external.tl.phate, and sc.tl.umap, then inspect the returned obs and uns entries. Document the embedding fields and parameter dictionaries, and determine a consistent representation for the tsne and umap metadata; done means the documentation and behavior are consistent.