Allow table columns and add_column to specify column class

[rly]

Motivation

Address #435

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov]

Codecov Report

Merging #436 into dev will increase coverage by 0.01%.
The diff coverage is 84.61%.

@@            Coverage Diff             @@
##              dev     #436      +/-   ##
==========================================
+ Coverage   80.09%   80.10%   +0.01%     
==========================================
  Files          34       34              
  Lines        7233     7237       +4     
  Branches     1584     1585       +1     
==========================================
+ Hits         5793     5797       +4     
  Misses       1059     1059              
  Partials      381      381              

Impacted Files	Coverage Δ
src/hdmf/common/table.py	83.58% <84.61%> (+0.11%)	⬆️

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[rly]

This is necessary for https://github.com/rly/ndx-genotype