API for exposing blocked ips to external applications

This is for use in main applications or admin interfaces for unblocking ips. The client will be another separate gem (that will be included here for testing, as a dev dependency).

 - endpoint for listing ips
 - endpoint for unblocking a specific ip

Webmachine is the framework used, as it's simple and straightforward. Webrick is used as the server, for now unless we see a reason to switch.

@kigster @sax