Fix #154 . Add copy/deepcopy methods for DataChunk and add tests

[oruebel]

Motivation

Fix #154 copy and deepcopy for data chunk and add tests for DataChunk

Checklist

• Have you checked our Contributing document?
• Have you ensured the PR description clearly describes problem and the solution?
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[codecov]

Codecov Report

Merging #155 into dev will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #155      +/-   ##
==========================================
+ Coverage   69.75%   69.78%   +0.03%     
==========================================
  Files          29       29              
  Lines        5736     5743       +7     
  Branches     1352     1352              
==========================================
+ Hits         4001     4008       +7     
  Misses       1307     1307              
  Partials      428      428

Impacted Files	Coverage Δ
src/hdmf/data_utils.py	84.06% <100%> (+0.35%)	⬆️

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