Threat control LWRP

Cf. first commit and README changes:

Add a threat_control LWRP, allowing to whitelist/blacklist IPs on CloudFlare
* Stores last action in a node attribute cache, CF API is only called once per day, or if status changes
* IP attribute defaults to current's node IP address
Hmm… good point, I'll add a possibility to control this with a node attribute.
:construction: 

Putting it in minutes would make sense, but will add some conversion bits to the code, Ruby's `DateTime` (used here) arithmetics working with days.