* modify zadd calls for redis-py 3.0

redis-py 3.0 changes the zadd interface that accepts a single
mapping argument that is expected to be a dict.
https://github.com/andymccurdy/redis-py#mset-msetnx-and-zadd

* change FailedQueue.push_job_id to always push a str

redis-py 3.0 does not attempt to cast values to str and is left
to the user.

* remove Redis connection patching

Since in redis-py 3.0, Redis == StrictRedis class, we no longer
need to patch _zadd and other methods.
Ref: https://github.com/rq/rq/pull/1016#issuecomment-441010847

My editor (atom) reads the setup.cfg but doesn't parse the cmd-line args in the
tox.ini. So lets move the flake8 config to setup.cfg.

Conflicts:
	rq/utils.py
	rq/worker.py
	setup.cfg
	setup.py

This reverts commit 1ab8c19696cb6b437729401640d00fd682e96b27 and
reintroduces all changes made by @dstufft.

Still, it needs more patches to reeanble the default log-to-console
behaviour.  See #121.

This reverts the commit range f367c38..978ba2d.

Issue #121 is currently blocking the 0.3.1 release.