Replace StyleCI with PHP CS Fixer

[mspirkov]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌
Fixed issues	comma-separated list of tickets # fixed by the PR, if any

[codecov]

Codecov Report

❌ Patch coverage is 87.17949% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.73%. Comparing base (d8b3c63) to head (6a8a540).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/FileHelper.php	86.48%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #104   +/-   ##
=========================================
  Coverage     93.73%   93.73%           
  Complexity      155      155           
=========================================
  Files             4        4           
  Lines           335      335           
=========================================
  Hits            314      314           
  Misses           21       21           

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