Move database classes and functions from kojihub.py to koji/db.py
Move QueryProcessor, InsertProcessor, UpdateProcessor,
BulkInsertProcessor, _applyQueryOpts, get_event, _dml,
_fetchMulti, _fetchSingle, _singleValue, _multiRow, _singleRow
Update koji-sweep-db script to DB Processors
Fixes: https://pagure.io/koji/issue/3466