Add support for PHP 8

[MilanPala]

• Droped Kdyby/StrictObjects, replaced by Nette/SmartObject.
• Unmaintaned Kdyby/CodingStandard replaced by Doctrine/CodingStandard.
• Allowed Symfony/EventDispatcher 4.3 where is some break, run tests please.
• Travis run only PHP 7.3, is there any plan for migrating to GHA?

[Spamercz]

Changes were cherrypicked and added do master - PHP 8 support https://github.com/Kdyby/Console/releases/tag/v3.0.0