Bulk element transcriptions

Fixes #322 (closed)

Benchmark

Using the local database (scripts)

./push_bulk_base.py  # Pushing transcriptions only (Bulk endpoint v1)
[INFO] Pushed 499 transcriptions in 0:00:00.709239
./push_sep.py        # Pushing elements and their transcription separately
100%|█████████████████████████████████████████████████████████████████| 499/499 [02:47<00:00,  2.98it/s]
[INFO] Pushed 499 transcriptions in 0:02:47.239785
./push_bulk_v2.py    # Bulk endpoint v2
[INFO] Pushed 499 transcriptions in 0:00:04.592675