queue/redis: implement QFactory for redismq

Related to #642.
queue: register redismq factory

Related to #642.
queue/redismq: unexport RedismqQ

Related to #642.
queue/redismq: implement handler

Related to #642.
queue: add test to ensure that redismqQFactory is registered

I was on vacation, I don't write tests anymore.

Closes #642.