Split different tests into submodules

[lgoettgens]

Still work in progress.

I try to wrap every logical block into its own module, as it is already the case for Piracy. This should help to be less confused about where some weird functions belong. And it declutters the tab-completion for Aqua..

[codecov]

Codecov Report

❌ Patch coverage is 89.65517% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.19%. Comparing base (94a9c7a) to head (7376d10).
⚠️ Report is 119 commits behind head on master.

Files with missing lines	Patch %	Lines
src/piracy.jl	55.55%	4 Missing ⚠️
src/project_extras.jl	50.00%	2 Missing ⚠️
src/ambiguities.jl	91.66%	1 Missing ⚠️
src/undefined_exports.jl	90.90%	1 Missing ⚠️
src/utils.jl	96.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
+ Coverage   77.07%   77.19%   +0.12%     
==========================================
  Files          11       11              
  Lines         724      728       +4     
==========================================
+ Hits          558      562       +4     
  Misses        166      166              

Flag	Coverage Δ
unittests	77.19% <89.65%> (+0.12%)	⬆️

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