Fix to_hierarchical_dataframe with VectorIndex data columns

[oruebel]

Motivation

Fix #665

Add check in to_hierarchical_dataframe to convert list and np.ndarray objects in the index to tuples. Since list and np.ndarray are not hashable this leads to a TypeError when creating the pandas.MultiIndex. By converting these items to tuples we can avoid this problem. This issue occurs if a hierarchical table contains VectorIndex columns as part of regular data columns, rather than indexed DynamicTableRegion columns which are resolved separately.

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
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[codecov]

Codecov Report

Merging #666 (e2e950b) into dev (56851ed) will increase coverage by 0.11%.
The diff coverage is 100.00%.

❗ Current head e2e950b differs from pull request most recent head 2a99016. Consider uploading reports for the commit 2a99016 to get more accurate results

@@            Coverage Diff             @@
##              dev     #666      +/-   ##
==========================================
+ Coverage   86.44%   86.55%   +0.11%     
==========================================
  Files          42       42              
  Lines        8562     8484      -78     
  Branches     1850     1847       -3     
==========================================
- Hits         7401     7343      -58     
+ Misses        832      806      -26     
- Partials      329      335       +6     

Impacted Files	Coverage Δ
src/hdmf/common/hierarchicaltable.py	100.00% <100.00%> (ø)
src/hdmf/build/objectmapper.py	91.87% <0.00%> (-0.50%)	⬇️
src/hdmf/container.py	89.98% <0.00%> (-0.06%)	⬇️
src/hdmf/data_utils.py	88.92% <0.00%> (-0.04%)	⬇️
src/hdmf/backends/hdf5/h5tools.py	82.05% <0.00%> (-0.02%)	⬇️
src/hdmf/utils.py	96.44% <0.00%> (-0.02%)	⬇️
src/hdmf/spec/namespace.py	87.57% <0.00%> (ø)
src/hdmf/common/__init__.py	75.83% <0.00%> (ø)
src/hdmf/common/resources.py	89.77% <0.00%> (+6.24%)	⬆️

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