Add support for odk:recordaudio

[seadowg]

Closes #517

Why is this the best possible solution? Were any other approaches considered?

I'm not that familiar with the code base so would not be surprised if there's a better way of parsing the parameters than what I ended up with. Mostly just put this in following how other actions/questions were handled.

What are the regression risks?

Shouldn't be any really as most code refers to a new question type.

Before submitting this PR, please make sure you have:

• [x] included test cases for core behavior and edge cases in tests_v1
• [x] run nosetests and verified all tests pass
• [x] run black pyxform to format code
• [x] verified that any code or assets from external sources are properly credited in comments

[codecov-io]

Codecov Report

Merging #519 (80fc54e) into master (7e86931) will increase coverage by 0.06%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #519      +/-   ##
==========================================
+ Coverage   83.86%   83.92%   +0.06%     
==========================================
  Files          25       25              
  Lines        3699     3713      +14     
  Branches      862      865       +3     
==========================================
+ Hits         3102     3116      +14     
  Misses        452      452              
  Partials      145      145              

Impacted Files	Coverage Δ
pyxform/question_type_dictionary.py	57.14% <ø> (ø)
pyxform/constants.py	100.00% <100.00%> (ø)
pyxform/xls2json.py	78.65% <100.00%> (+0.32%)	:arrow_up:

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[lognaturel]

@MartijnR it occurs to me you might like (and it might be a good idea) to do a sanity check on this.

[MartijnR]

Thanks. I had a quick look at the tests. All looks good to me!