add ontology helper

[dsavchenko]

No description provided.

[codecov]

Codecov Report

Merging #223 (fea3dc8) into master (3688a73) will increase coverage by 2.91%.
The diff coverage is 90.78%.

@@            Coverage Diff             @@
##           master     #223      +/-   ##
==========================================
+ Coverage   54.68%   57.59%   +2.91%     
==========================================
  Files          20       22       +2     
  Lines        4316     4674     +358     
==========================================
+ Hits         2360     2692     +332     
- Misses       1956     1982      +26     

Files	Coverage Δ
tests/test_ontology.py	100.00% <100.00%> (ø)
oda_api/ontology_helper.py	85.46% <85.46%> (ø)

... and 2 files with indirect coverage changes