Save sample set object with metadata keys

[charleshtrenholm]

Saves time in populating dynamic dropdowns by storing metadata keys in sample set instead of only within the samples themselves.

[codecov]

Codecov Report

Merging #116 (7bbdd17) into master (91b860f) will decrease coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #116      +/-   ##
==========================================
- Coverage   82.44%   82.34%   -0.10%     
==========================================
  Files          12       12              
  Lines        1447     1439       -8     
==========================================
- Hits         1193     1185       -8     
  Misses        254      254              

Impacted Files	Coverage Δ
lib/sample_uploader/sample_uploaderImpl.py	79.22% <ø> (-0.12%)	⬇️
lib/sample_uploader/utils/mappings.py	85.84% <ø> (ø)
lib/sample_uploader/utils/sample_utils.py	76.76% <ø> (-0.75%)	⬇️
lib/sample_uploader/utils/importer.py	88.04% <100.00%> (+0.08%)	⬆️

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