fixed related_by_category finder to exclude target obj and fixed url check in clean method of publishable
Merge pull request #157 from MichalMaM/fix_related_finder_and_publishable_clean

Fixed related_by_category finder and Publishable URL uniqueness check.
Reverting a bad commit.

This reverts commit 41a6b18efcadcd4e5384bfa29263807fddcb0122.