Tests

[NeoTheThird]

This replaces mocha+sinon+chai+sinonChai+coverage with jest for better electron testing and adds some basic unit tests. Code coverage is abysmal, naturally, but this is only just the beginning.

[codecov-io]

Codecov Report

Merging #1553 (8f0e40f) into master (24050ee) will decrease coverage by 71.67%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #1553       +/-   ##
===========================================
- Coverage   97.24%   25.57%   -71.68%     
===========================================
  Files           2       14       +12     
  Lines         218      657      +439     
===========================================
- Hits          212      168       -44     
- Misses          6      489      +483     

Impacted Files	Coverage Δ
src/lib/asarLibs.js	100.00% <ø> (ø)
src/lib/cache.js	54.54% <0.00%> (-35.11%)	⬇️
src/lib/log.js	100.00% <0.00%> (ø)
src/report.js	22.22% <0.00%> (ø)
src/lib/deviceTools.js	55.55% <0.00%> (ø)
src/lib/updater.js	38.88% <0.00%> (ø)
src/main.js	25.00% <0.00%> (ø)
src/lib/system-image.js	17.14% <0.00%> (ø)
src/lib/errors.js	45.45% <0.00%> (ø)
src/lib/settings.js	75.00% <0.00%> (ø)
... and 5 more

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