Resolve "Detect anomaly in user access pattern"

Closes #308 (closed) At each sign-in audit information (IP, browser details) is collected and audit is performed if sufficient data is present. Audit is based on scoring composed of changes in IP, IP-country (using MaxMind free GeoIP database) - details in comments. If result is negative user is notified via mail. There is a set of RSpec tests including condition that should (or should not) trigger audit failure. Also I've done some manual testing.