Feature request: Block access to certain tables

Similar to the `EXPLORER_SQL_BLACKLIST`, I would love a feature that would enable blocking queries to specific tables (e.g. auth_user, authtoken_token, django_session, etc.). I know the correct way to do this is to only grant select access to the correct tables for the read only database account being used for the SQL Explorer connection. But as with `EXPLORER_SQL_BLACKLIST`, in some use cases, setting those permissions may not be available.

Sample logic:
```
def passes_table_blacklist(sql: str) -> Tuple[bool, Iterable[str]]:
blocked_tables = getattr(settings, 'EXPLORER_TABLE_BLACKLIST', [])
failed_tables = [table.upper() for table in blocked_tables if table.upper() in sql.upper()]
return bool(failed_tables), failed_tables
```

Compare to [passes_blacklist](https://github.com/explorerhq/sql-explorer/blob/910cb710ab4015d3ad32e4c63b9263e7381bd19f/explorer/utils.py#L22).