[Dev Tools NG] Problematic entries in .ratings files

The following problematic entries are generated when applying the new rating system

• Entry for .ratings file: The file should be ignored by the ratings generator, since otherwise there will be local modifications when reapplying the rating generator to an unmodified source folder until a fixed point is reached
• Consider if .ratings file should be omitted for empty directories. E.g., currently, the files are generated when applying the ratings for an entire source src folder

(from redmine: issue id 3194, created on 2017-11-28, closed on 2017-12-08)