Simplify code for persisting entities by cascading this operation from primary entity.

No functional changes.
Updated checkstyle-suppressions.xml file to fix CheckStyle warnings.

Should be in d3efec5558176ec3e8a1da64875485844c92eb30 commit.

No functional changes.
Extracted interfaces of service classes.

Also changed ImageService.save() method visibility from protected to public.

No functional changes.