588 Add check on file export to ensure all required properties are filled out

[ehennestad]

Fix #588

Motivation

Check that all required properties are filled out before nwb file is exported

How to test the behavior?

nwb=NwbFile();
nwbExport(nwb, 'test.nwb')

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.90%. Comparing base (5cd6af6) to head (99d8b42).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #600      +/-   ##
==========================================
+ Coverage   90.56%   90.90%   +0.34%     
==========================================
  Files         107      107              
  Lines        4695     4751      +56     
==========================================
+ Hits         4252     4319      +67     
+ Misses        443      432      -11     

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[ehennestad]

@bendichter Some fixes to the workflows from the previous PR got included here.