#48 - custom fixers added

[krzysztofrewak]

I added following:

PhpCsFixerCustomFixers\Fixer\ConstructorEmptyBracesFixer;
PhpCsFixerCustomFixers\Fixer\InternalClassCasingFixer;
PhpCsFixerCustomFixers\Fixer\MultilinePromotedPropertiesFixer;
PhpCsFixerCustomFixers\Fixer\NoUselessCommentFixer;
PhpCsFixerCustomFixers\Fixer\PhpdocArrayStyleFixer;
PhpCsFixerCustomFixers\Fixer\PromotedConstructorPropertyFixer;
PhpCsFixerCustomFixers\Fixer\SingleSpaceAfterStatementFixer;
PhpCsFixerCustomFixers\Fixer\SingleSpaceBeforeStatementFixer;
PhpCsFixerCustomFixers\Fixer\StringableInterfaceFixer;

I found out that nullable readonly properties are not working as we would expect; I created issue here (PHP-CS-Fixer/PHP-CS-Fixer#6221) and it was fixed here (PHP-CS-Fixer/PHP-CS-Fixer#6224), but for some reasons it's still not working with ECS underneath our Codestyle.

It should close #48.