Extend validator to check if all required parameters are present in p…

[dweindl]

…arameter table (Closes #43)

[codecov-io]

Codecov Report

Merging #159 into develop will decrease coverage by 0.51%.
The diff coverage is 53.57%.

@@             Coverage Diff             @@
##           develop     #159      +/-   ##
===========================================
- Coverage    71.78%   71.27%   -0.52%     
===========================================
  Files           12       12              
  Lines         1159     1173      +14     
  Branches       265      268       +3     
===========================================
+ Hits           832      836       +4     
- Misses         279      289      +10     
  Partials        48       48

Impacted Files	Coverage Δ
petab/lint.py	50.22% <21.42%> (-1.95%)	⬇️
petab/core.py	79.88% <85.71%> (+0.11%)	⬆️

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[erikadudki]

looks good