The partial class ClientController had two constructors declared
across ClientController.cs and ClientController.Collections.cs.
ASP.NET Core DI failed to pick one at request time with:
System.InvalidOperationException: Multiple constructors accepting
all given argument types have been found in type
'Yavsc.Controllers.ClientController'.
Move IHtmlLocalizer<ClientController> into the primary constructor
in ClientController.cs and drop the duplicate one in
ClientController.Collections.cs. The Collections partial now keeps
only its readonly field and action methods; the constructor and
field assignment are unified on the main file.
Also add the missing 'using Microsoft.AspNetCore.Mvc.Localization;'
to ClientController.cs so IHtmlLocalizer resolves.
