Move redis_connect to database module (fix #49 issue)

`import redis` in the __init__.py file make the setup.py not
loadable without redis lib already installed.
Move TEST_CONNECTION_SETTINGS to tests/base.py
Make "redis_connect" a method of Database
Merge pull request #51 from yohanboniface/move_redis_connect

Move redis_connect to database module (fix #49 issue)