refactoring

src/main/java/fil/sr2/flopbox/FTPResource.java

src/main/java/fil/sr2/flopbox/FTPServerRepository.java

src/main/java/fil/sr2/flopbox/FTPService.java

src/main/java/fil/sr2/flopbox/utils/AuthFilter.java

src/main/java/fil/sr2/flopbox/utils/FTPClientFactory.java

src/main/java/fil/sr2/flopbox/utils/FTPException.java

src/main/java/fil/sr2/flopbox/utils/FTPServerConfig.java