Use dictionary for dorks storage with regular dumps to json file

While rewriting the dork_db with sqlalchemy i realized that the dorks database does not in any way justify using a full-blown RDBMS... So here goes my take on a much more simple and maintainable approach.

From commit message:
- Complete rewrite of dork_db.py.
- Dorks are now completely stored in memory.
- Every 10'th update the memory representation gets dumped to a JSON file.