fitting/analysis improvements

[pkienzle]

• increase batch size for faster gpu
• use umap rather than t-SNE for manifold learning if available (it's faster)
• use 'ward' for dendrogram linkage
• use optimal ordering on dendrogram
• use dendrogram ordering on manifold plot
• support tensorflow 1.5 as well as 2.1
• use time interval for checkpointing