Allow writing OME TIFF files containing multichannel optical microscopy time series

[Tom Goddard]

Would like to be able to write out optical microscopy data including multiple channels and time series to a single file. OME TIFF seems like the format with best cross application support. Add support for writing this format. Unfortunately tifffile.py that we use to read OME TIFF does not appear support writing it. Maybe we can use the C++ library from OME, although that might be a lot of work if Python bindings are not available.