Aligned textgrids now pickleable

[JoFrhwld]

Previous update to clone classes within AlignedTextGrids broke pickleability

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.56%. Comparing base (192e2d1) to head (4461a5a).
Report is 8 commits behind head on dev.

❗ Current head 4461a5a differs from pull request most recent head abacab1

Please upload reports for the commit abacab1 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #183      +/-   ##
==========================================
+ Coverage   89.53%   89.56%   +0.02%     
==========================================
  Files          14       14              
  Lines        1319     1322       +3     
==========================================
+ Hits         1181     1184       +3     
  Misses        138      138              

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