Add more metabolic model tests

[stelmo]

Add metabolite tests and neaten the consistency tests

[exaexa]

Pretty much okay, only minor/stylish fixes required.

Regarding the @test infrastructure -- let's not do this in this PR so that we have something working asap; I'll need to solve the test-in-test problem first probably utilizing some kind of dummy AbstractTestSet, then I'll convert it.

[exaexa]

PS please separate all Memote tests into their own PRs. The list here would probably make a good tracking issue.

[stelmo]

/format

[github-actions]

✔️ Auto-formatting triggered by this comment succeeded, commited as ea30a31

[codecov-commenter]

Codecov Report

Base: 33.16% // Head: 47.87% // Increases project coverage by +14.70% 🎉

Coverage data is based on head (1008760) compared to base (652af5e).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 1008760 differs from pull request most recent head ea30a31. Consider uploading reports for the commit ea30a31 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #19       +/-   ##
===========================================
+ Coverage   33.16%   47.87%   +14.70%     
===========================================
  Files           3        4        +1     
  Lines         202      259       +57     
===========================================
+ Hits           67      124       +57     
  Misses        135      135               

Impacted Files	Coverage Δ
src/memote/consistency.jl	93.90% <100.00%> (ø)
src/memote/metabolites.jl	100.00% <100.00%> (ø)

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[stelmo]

/format

[github-actions]

✔️ Auto-formatting triggered by this comment succeeded, commited as 4a74e0c

[exaexa]

🚀