WIP: First refactor to then recursively find ALL hyponyms
Refactor tag_preprocessing::parse_json_data to use flags
Revert "Refactor tag_preprocessing::parse_json_data to use flags"

This reverts commit a93afd3cab57143be1bfa47f33c6ebafcd90d68b.
Add method to recursively fetch hyponyms for synset_name
find_hyponyms_on_wordnet now returns full hyponym tree for word
Add method to build reverse tag index for photos

Returns dictionary:
  {
    "tag1": [photo_id1, photo_id2, ...]
    "tag2": [photo_id3, photo_id1, ...]
  }