Add support for OME-Zarr image format

Since we started using Zarr format before the OME-Zarr standard was a thing we have diverged from them.

We need to add support for OME-Zarr files. This should not take long and in the first instance we will need to support our own Zarr format (as produced by imc2zarr) and the current standard OME-Zarr.