Updated usage in README.md [Fix Limenius#24]

Merge pull request Limenius#23 from MyOnlineStore/master

fixed dockblocks, updated readme, enabled travis phpcs

Symfony 4 allowed in composer.json

Relax requirements for symfony translator

Transformers can translate labels and descriptions [fix Limenius#8]

Fix in checkbox serialization [Fixes Limenius#7]

buildLiform() affects the schema, does not add a subarray

Validator guessing

Fix ArrayTransfomrmer to render more than one child if present

More compatible tests