allow user to specify their own "channel name" in an hdf5 cutout

[alexbaden]

User story: I have a generic script that takes a single channel in an HDF5 file, does some data analysis, and writes it out. I wrote my script for OCP v0.6 which used "CUTOUT" as every channel name. Or, maybe I am an AT user and want to run my script across multiple channels. I'll either have to change the channel name in the source code and recompile, specify it as a command line parameter, or do some sort of fancy HDF5 search to figure out what the group for my data in the HDF5 is (e.g. /DAPI/CUTOUT or /EM/CUTOUT or /WHATEVER/CUTOUT ).

Proposal: Provide the following interface: /ocp/ca/<>/<>/hdf5{<<NAME OF GROUP>>}/<>

So one could write: /ocp/ca/kasthuri11/image/hdf5{DATA}/<> and get data in /DATA/CUTOUT

I am writing this because it's going to wreak havoc with how I've deved the surfaces stuff. And I already have to take in a ton of command line parameters, so I'm trying to limit that when possible. I believe we only allow one cutout per HDF5 file, so that shouldn't be a problem, but one imagine a few solutions for that. What say you? I could probably implement, but would certainly need @kunallillaney help.

( @jovo @willgray @j6k4m8 @Aeusman -- any of you use this? )