add a redis container to cache status runs

[ruebenramirez]

• set default expire to 20 seconds
• add a "cache flush" route to remove all redis keys
• add redis-simple-cache around retrieving main get_status() resutls in places like https://github.com/ruebenramirez/nest_thermostat/blob/master/nest_thermostat/__init__.py#L92

[ruebenramirez]

redis-simple-cache plugin on pypi:
https://pypi.python.org/pypi/redis-simple-cache/0.0.1

[ruebenramirez]

custom redis host required eyeing the source for the SimpleCache class....
https://github.com/vivekn/redis-simple-cache/blob/master/redis_cache/rediscache.py