Add disable send policy (#1130)

* Add Disable Send policy

* Test DisableSend policy

* PR Review

* Update tests for using CurrentContext

This required making an interface for CurrentContext and mocking out
the members used. The interface can be expanded as needed for tests.

I moved CurrentContext to a folder, which changes the namespace
and causes a lot of file touches, but most are just adding a reference

* Fix failing test

* Update exemption to include all exempt users

* Move all CurrentContext usages to ICurrentContext

* PR review. Match messaging with Web

src/Core/Identity/UserStore.cs

@@ -5,6 +5,7 @@ using Microsoft.AspNetCore.Identity;
 using Bit.Core.Models.Table;
 using Bit.Core.Repositories;
 using Bit.Core.Services;
+using Bit.Core.Context;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Bit.Core.Identity
@@ -18,12 +19,12 @@ namespace Bit.Core.Identity
     {
         private readonly IServiceProvider _serviceProvider;
         private readonly IUserRepository _userRepository;
-        private readonly CurrentContext _currentContext;
+        private readonly ICurrentContext _currentContext;
 
         public UserStore(
             IServiceProvider serviceProvider,
             IUserRepository userRepository,
-            CurrentContext currentContext)
+            ICurrentContext currentContext)
         {
             _serviceProvider = serviceProvider;
             _userRepository = userRepository;