Fix ensemble simulate and calibrate.

[jClugstor]

Ensemble simulate now takes a collection of models and a collection of weights and constructs a solution which is a linear combination of the solutions and the weights. Ensemble calibrate does this in reverse, taking a dataset and a collection of models, and gives the weights that produce the dataset. Closes #109

[jClugstor]

This also adds tests for server routes.

[codecov-commenter]

Codecov Report

Merging #133 (9cd5c37) into main (1d4c836) will increase coverage by 0.54%.
Report is 9 commits behind head on main.
The diff coverage is 79.62%.

@@            Coverage Diff             @@
##             main     #133      +/-   ##
==========================================
+ Coverage   77.99%   78.53%   +0.54%     
==========================================
  Files           3        3              
  Lines         409      452      +43     
==========================================
+ Hits          319      355      +36     
- Misses         90       97       +7     

Files	Coverage Δ
src/SimulationService.jl	70.98% <70.58%> (+0.68%)	⬆️
src/operations.jl	88.26% <83.78%> (-0.50%)	⬇️

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[joshday]

One thing we want is to have all the data/test cases live at https://github.com/darpa-askem/simulation-integration so that we don't need to maintain them, keep them in sync with the latest AMR versions, etc.

Can you split the JSON/CSV out from this PR and make a PR to add them in https://github.com/darpa-askem/simulation-integration? Then change the tests here to download what we need from there.