Migrated DomainsApiController

Moved action to exiting ContentController, moved viewmodels out into seperate files.

src/Umbraco.Web/Models/ContentEditing/DomainDisplay.cs

@@ -0,0 +1,16 @@
+namespace Umbraco.Web.Models.ContentEditing
+{
+    public class DomainDisplay
+    {
+        public DomainDisplay(string name, int lang)
+        {
+            Name = name;
+            Lang = lang;
+        }
+
+        public string Name { get; }
+        public int Lang { get; }
+        public bool Duplicate { get; set; }
+        public string Other { get; set; }
+    }
+}