Fixed qu, queue_classic, sneakers adapters

This fixes the bugs I found while working on the integration testing at #102

qu:
- job class is converted to string when serialized by qu's backend
- because of the way the queue name was handled internally by qu the jobs were always run from the default queue

queue_classic:
- job class is converted to string when serialized by queue_classic's backend

sneakers:
- because sneakers' `.enqueue` publishes directly to MQ it should only receive one argument which is a string