Add CS checker and fixer

[roxblnfk]

Add CS checker and fixer that will:

• [x] Check the code for compliance with PER-2 https://github.com/buggregator/trap/pull/67
• [x] #68
• Take into account some custom aspects:
  • We use FQN for functions in the global namespace
  • We use FQN for classes in the global namespace

https://github.com/PHP-CS-Fixer/PHP-CS-Fixer