Enh/device description

[ajtritt]

Motivation

After #695, Device became a group with a help string. This PR adds a required description field. A Device ObjectMapper was also included for setting a default value for those files generated prior to this change.

This change was inspired by discussions with @ageorgou

Checklist

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[oruebel]

Looks like some of tests need to be updated, but other than that it looks good to me.

[bendichter]

I prefer these types of additions to be optional. This change will require changes to dozen different conversion scripts and does not offer me much utility. I don't think these types of descriptive fields need to be required

[ajtritt]

Then we should just remove Device. A group with a name and a constant help string doesn’t do much.

[codecov]

Codecov Report

Merging #723 into dev will increase coverage by 2.2%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##              dev     #723     +/-   ##
=========================================
+ Coverage   72.29%   74.49%   +2.2%     
=========================================
  Files          36       60     +24     
  Lines        2718     6905   +4187     
  Branches      513     1444    +931     
=========================================
+ Hits         1965     5144   +3179     
- Misses        632     1355    +723     
- Partials      121      406    +285

Impacted Files	Coverage Δ
src/pynwb/device.py	100% <100%> (ø)	⬆️
src/pynwb/epoch.py	73.13% <0%> (-9.22%)	⬇️
src/pynwb/__init__.py	69.49% <0%> (-2.55%)	⬇️
src/pynwb/core.py	70.51% <0%> (-0.87%)	⬇️
src/pynwb/icephys.py	88.88% <0%> (-0.4%)	⬇️
src/pynwb/ecephys.py	97.27% <0%> (-0.1%)	⬇️
src/pynwb/ogen.py	100% <0%> (ø)	⬆️
src/pynwb/behavior.py	100% <0%> (ø)	⬆️
src/pynwb/validate.py	0% <0%> (ø)	⬆️
src/pynwb/retinotopy.py	100% <0%> (ø)	⬆️
... and 32 more

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[bendichter]

making Device optional obviates the Device io file

[bendichter]

The addition of description to the tests is now superfluous, but I don't mind leaving them

fixed

[bendichter]

Why is this a dataset and not an attribute? I would not expect this to be changed once it is written, so shouldn't it be an attribute (NeurodataWithoutBorders/nwb-schema#48)? Making this required would be a schema-breaking change, so I would like to make this optional.