extract FileStorageService to separate file storage logic
- extraction is done
- unit tests are working
fix integration tests by setting autowired constructor
extract mark as deleted stuf as well
refactor repomdgenerator to use filestorageservice
fix RepoMdGeneratorTest
rename GridFsFileDescriptor
remove dependency of FileDescriptor to GridFsDBFile
remove dependencies on GridFsDBFile
extract FileStorageService tests
remove dependency to GridFSDBFile
remove dependency to GridFSDBFile