Check inventory object identity on import and update from Git repositories

Current Situation

• When importing objects from export archive files (.zip, tar.gz) and when updating inventory objects from a Git repository, then available objects will overwrite inventory objects. This includes to overwrite identical inventory objects.
• As a result inventory objects will be marked as "draft" though there is no difference between the imported object and an existing inventory object.

Desired Behavior

• Both operations to import from export archive files and to update inventory objects from a Git repository should check object identity and should not modify the status of an existing inventory object that is identified being identical.
• The implementation will create hashes for objects and will compare hash values.