488 move parsing methods from host to api clients

[maciekbanas]

Closes #459
Closes #488

[codecov]

Codecov Report

Attention: Patch coverage is 89.55696% with 33 lines in your changes missing coverage. Please review.

Project coverage is 70.91%. Comparing base (f53947e) to head (9defa4c).
Report is 5 commits behind head on devel.

Files with missing lines	Patch %	Lines
R/EngineRestGitLab.R	70.37%	16 Missing ⚠️
R/EngineGraphQLGitHub.R	95.28%	5 Missing ⚠️
R/EngineGraphQLGitLab.R	95.91%	4 Missing ⚠️
R/GitStats.R	60.00%	4 Missing ⚠️
R/GitHost.R	80.00%	2 Missing ⚠️
R/EngineRestGitHub.R	94.11%	1 Missing ⚠️
R/GitHostGitLab.R	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            devel     #503      +/-   ##
==========================================
- Coverage   70.92%   70.91%   -0.01%     
==========================================
  Files          17       17              
  Lines        3061     3067       +6     
==========================================
+ Hits         2171     2175       +4     
- Misses        890      892       +2     

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