Generalized Image Stack translator class

[ssomnath]

The current PtychographyTranslator, MovieTranslator, OneViewTranslator, ImageTranslator share a fair number of pieces in common. Perhaps a generalized class could be created that would be able to:

1. Maximize code reuse
2. Minimize effort required to write variants of an image stack translator

Also, Dask may come in handy when reading numerous image files, pre-processing (e.g. - binning) in memory and writing the data into HDF5 datasets.

Related to: #197, #196, #194