Allow string inputs for most interfaces

[lawrence-mbf]

Fixes #287

Motivation

Allow for strings since these may be used by users.

How to test the behavior?

Using any of the generateCore, generateExtension, nwbRead, or nwbExport with double-quotes instead of single quotes should not cause errors.

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

Merging #522 (f48a5d6) into master (461c5c4) will decrease coverage by 0.05%.
The diff coverage is 84.12%.

@@            Coverage Diff             @@
##           master     #522      +/-   ##
==========================================
- Coverage   87.89%   87.84%   -0.05%     
==========================================
  Files         129      129              
  Lines        5461     5489      +28     
==========================================
+ Hits         4800     4822      +22     
- Misses        661      667       +6     

Files Changed	Coverage Δ
nwbExport.m	55.55% <55.55%> (-15.88%)	⬇️
nwbRead.m	79.38% <80.85%> (+0.49%)	⬆️
generateExtension.m	90.32% <90.32%> (-2.54%)	⬇️
generateCore.m	95.45% <95.45%> (+0.21%)	⬆️
+types/+untyped/DataStub.m	95.15% <100.00%> (+0.08%)	⬆️
+types/+untyped/ExternalLink.m	95.77% <100.00%> (+0.25%)	⬆️
+types/+untyped/ObjectView.m	88.00% <100.00%> (+1.04%)	⬆️
+types/+untyped/SoftLink.m	91.42% <100.00%> (+0.80%)	⬆️

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