Constants: fixed six Checkstyle issues (mvn checkstyle:checkstyle)

- Fixed six Checkstyle issues (after running "mvn checkstyle:checkstyle" and checking "target\checkstyle-result.xml").
- Added @SuppressWarnings("UnusedDeclaration") annotations to the LIST_SORT_KEYS_DOUBLE and LIST_SORT_KEYS_INT constants that are unused while the new sorting code is in development.