HTTPS certificate validation options

New: Enable HTTPS certificate validation by default
New: Option to disable certificate validation for all or only local addresses

src/NzbDrone.Common/Extensions/IpAddressExtensions.cs

@@ -0,0 +1,29 @@
+using System.Net;
+
+namespace NzbDrone.Common.Extensions
+{
+    public static class IPAddressExtensions
+    {
+        public static bool IsLocalAddress(this IPAddress ipAddress)
+        {
+            if (ipAddress.ToString() == "::1")
+            {
+                return true;
+            }
+
+            byte[] bytes = ipAddress.GetAddressBytes();
+            switch (bytes[0])
+            {
+                case 10:
+                case 127:
+                    return true;
+                case 172:
+                    return bytes[1] < 32 && bytes[1] >= 16;
+                case 192:
+                    return bytes[1] == 168;
+                default:
+                    return false;
+            }
+        }
+    }
+}