Better handling of multiple image ratios

[grio43]

Currently a decent amount dropped from the buckets. Would be nice to allow buckets smaller than the batch size to not be dropped or buckets even of 1 item to be allowed.

Just having off batches that might be smaller than the target batch size. When unable to meet the batch size. Also for allowing not square ratios to have a minimum height and minimum width.

[miasik]

Take a look there:
#975