Post concept set

[gowthamrao]

Addresses https://github.com/OHDSI/ROhdsiWebApi/issues/106

With this PR we are able to post definitions of Cohorts and ConceptSets.

• this code will check if a name assigned to the expression in the target WebApi - exists in the target WebApi (if yes, throws an error)
• posts the expression. If failed, it will return error message. If success, it will return details of the posted expression.

This framework is working for cohort and conceptset, but not incidence rate, pathways, cohort characterization, estimation or prediction. Tagging @chrisknoll @anthonysena - as i may need guidance from you two

@schuemie could you please review this code

[gowthamrao]

@schuemie i am having issues with R check and unit tests for now.

[codecov-commenter]

Codecov Report

Merging #116 into develop will decrease coverage by 40.09%. The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop    #116       +/-   ##
===========================================
- Coverage    40.09%   0.00%   -40.10%     
===========================================
  Files           12      12               
  Lines          873     897       +24     
===========================================
- Hits           350       0      -350     
- Misses         523     897      +374     

Impacted Files	Coverage Δ
R/Estimation.R	0.00% <0.00%> (ø)
R/WebApi.R	0.00% <0.00%> (-74.13%)	:arrow_down:
R/Concept.R	0.00% <0.00%> (-100.00%)	:arrow_down:
R/Private.R	0.00% <0.00%> (-100.00%)	:arrow_down:
R/ConceptSet.R	0.00% <0.00%> (-76.05%)	:arrow_down:
R/AutoGeneratedDefinitions.R	0.00% <0.00%> (-75.00%)	:arrow_down:
R/CohortDefinition.R	0.00% <0.00%> (-34.57%)	:arrow_down:

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