hdf5 equivalent of config_dumper

we need to have some kind of metadata in the hdf5 files. 

(normal tuples also don't have art metadata, so need it for them as well)

working on a header-only reader- has a specialized exception ERS package that may introduce more dependence than we want. 

Working on channel map. 

Compression out of the daq - do it on SSD?  Cost estimate?  LDRD