[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/Request/CipherRequest.cs

@@ -81,7 +81,8 @@ namespace Bit.Core.Models.Request
             {
                 Type = f.Type,
                 Name = f.Name?.EncryptedString,
-                Value = f.Value?.EncryptedString
+                Value = f.Value?.EncryptedString,
+                LinkedId = f.LinkedId,
             }).ToList();
 
             PasswordHistory = cipher.PasswordHistory?.Select(ph => new PasswordHistoryRequest