IMDB: Update import script, source files and dump (#12)

* Update script and source files
- Removed duplicate edges
- Removed empty fields ("")
- Removed a dummy edge
- Converted releaseDate to number, corrected timezone (was apparently assuming Europe/Berlin instead of UTC)
- Fixed 13 releaseDates manually
- Make the script work with ArangoDB 3.7/3.8
- Don't drop edge _key anymore (duplicates removed in source file)
- Add type: "Genre" to genre vertices
- Disable creation of fulltext indexes
* Update README
* Change source file extensions from .json to .jsonl
* Update dump

fixed imdb for latest arangodb version