Quality improvements

Added declaration virtual methods to Nil class, just for PHP Analyzer
Added cleanErrors() method for Crud package - just for tests
Updated comments blocks and codestyle
Updated phpunit configuration - changed configuration for calculate code coverage
Fixed LIKE filter in Grid\Source\ArraySource
Fixed readOne() in Controller\Rest
Removed unused USE statements
Removed duplicate code from Db\Query\Select
Refactoring Rest controller - replaced call http_response_code with Response instance