Refactor IP registrar restriction

#600

app/models/authorization/restricted_ip.rb

@@ -0,0 +1,25 @@
+module Authorization
+  class RestrictedIP
+    def initialize(ip)
+      @ip = ip
+    end
+
+    def self.enabled?
+      Setting.registrar_ip_whitelist_enabled
+    end
+
+    def can_access_registrar_area?(registrar)
+      return true unless self.class.enabled?
+      registrar.white_ips.registrar_area.include_ip?(ip)
+    end
+
+    def can_access_registrar_area_sign_in_page?
+      return true unless self.class.enabled?
+      WhiteIp.registrar_area.include_ip?(ip)
+    end
+
+    private
+
+    attr_reader :ip
+  end
+end