[Linked fields] Add Linked Field as a custom field type (#1563)

* Add linked fields support

* Fix style, don't show linked field if Secure Note

* Finish basic linked fields for Login

* Use Field.LinkedId to store linked field info

* Reset Linked Custom Fields if cipherType changes

* Refactor to use ItemView class

* Use enum for LinkedId

* Detect if no linkedFieldOptions

src/Core/Models/Data/FieldData.cs

@@ -12,10 +12,12 @@ namespace Bit.Core.Models.Data
             Type = data.Type;
             Name = data.Name;
             Value = data.Value;
+            LinkedId = data.LinkedId;
         }
 
         public FieldType Type { get; set; }
         public string Name { get; set; }
         public string Value { get; set; }
+        public LinkedIdType? LinkedId { get; set; }
     }
 }