Enhance selection of rows in DynamicTable

[oruebel]

Motivation

The goal is to enhance selection of rows from a DynamicTable. This PR makes the following changes:

• Add support for selecting rows in a DynamicTable via slice and add corresponding tests
• Return Pandas DataFrame when selecting full rows from a DynamicTable and add/update unit tests accordingly
• Use OrderedDict when converting to Pandas to ensure consistent ordering on columns

The matching PR that updates the tests in PyNWB is NeurodataWithoutBorders/pynwb#1106

Checklist

• Have you checked our Contributing document?
• Have you ensured the PR description clearly describes 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 #XXX notation where XXX is the issue number ? By including "Fix #XXX" you allow GitHub to close the corresponding issue.

[codecov]

Codecov Report

Merging #191 into dev will decrease coverage by <.01%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##              dev     #191      +/-   ##
==========================================
- Coverage   70.27%   70.26%   -0.01%     
==========================================
  Files          30       30              
  Lines        5920     5946      +26     
  Branches     1385     1394       +9     
==========================================
+ Hits         4160     4178      +18     
- Misses       1326     1330       +4     
- Partials      434      438       +4

Impacted Files	Coverage Δ
src/hdmf/common/table.py	55.66% <66.66%> (+0.92%)	⬆️

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[bendichter]

looks good to me!

[rly]

Looks good to me too

[oruebel]

Thanks @rly @bendichter for reviewing. Now I just need to get a matching PR going for PyNWB to make sure it works with these changes ;-)

[oruebel]

@rly can you review this PR again. In addition to the previous changes I had to add the DynamicTableRegion.shape property to make shape validation work with the new behavior (which is being used in PyNWB). Could you also review the matching PR in PyNWB NeurodataWithoutBorders/pynwb#1106 and help me with the merge/release of these PRs. I need these PRs in order to be able to merge oruebel/ndx-icephys-meta#13