Validation, settings UI cleanup and different settings models, oh my

New: Download client UI matches other settings
Fixed: Prevent drone factory folder from being set to invalid paths/root path for series
Fixed: Switching pages in settings will not hide changes
Fixed: Test download clients
Fixed: Settings are validated before saving

src/NzbDrone.Api/Config/IndexerConfigResource.cs

@@ -0,0 +1,12 @@
+using System;
+using NzbDrone.Api.REST;
+
+namespace NzbDrone.Api.Config
+{
+    public class IndexerConfigResource : RestResource
+    {
+        public Int32 Retention { get; set; }
+        public Int32 RssSyncInterval { get; set; }
+        public String ReleaseRestrictions { get; set; }
+    }
+}