Let users choose what type of burst data they download

[SpicyGarlicAlbacoreRoll]

• adds FileDownloadType to use with ASFProduct and ASFSearchResults download
• adds additionalUrls property to ASFProduct properties

[codecov-commenter]

Codecov Report

Merging #208 (c812cca) into master (77b9fb5) will decrease coverage by 0.74%. The diff coverage is 32.35%.

@@            Coverage Diff             @@
##           master     #208      +/-   ##
==========================================
- Coverage   89.50%   88.76%   -0.74%     
==========================================
  Files          51       52       +1     
  Lines        1934     1958      +24     
==========================================
+ Hits         1731     1738       +7     
- Misses        203      220      +17     

Flag	Coverage Δ
unittests	88.76% <32.35%> (-0.74%)	:arrow_down:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
asf_search/ASFProduct.py	59.67% <9.52%> (-22.15%)	:arrow_down:
asf_search/ASFSearchResults.py	74.50% <20.00%> (+0.50%)	:arrow_up:
asf_search/CMR/translate.py	95.58% <100.00%> (+0.02%)	:arrow_up:
asf_search/download/__init__.py	100.00% <100.00%> (ø)
asf_search/download/file_download_type.py	100.00% <100.00%> (ø)
asf_search/export/export_translators.py	100.00% <100.00%> (ø)