[Provider] Server entities and models (#1370)

* Mock out provider models and service

* Implement CreateAsync, CompleteSetupAsync, UpdateAsync, InviteUserAsync and ResendInvitesAsync

* Implement AcceptUserAsync and ConfirmUsersAsync

* Implement SaveUserAsync and DeleteUserAsync

* Add email templates

* Add admin operations for providers

* Fix mail template names

* Rename roles

* Verify provider has provideradmin

* Add self hosted check to admin controller

* Resolve review comments

* Update sql queries

* Change create provider to use email instead of userId

src/Admin/Models/ProviderViewModel.cs

@@ -0,0 +1,27 @@
+using System.Collections.Generic;
+using System.Linq;
+using Bit.Core.Enums.Provider;
+using Bit.Core.Models.Table.Provider;
+
+namespace Bit.Admin.Models
+{
+    public class ProviderViewModel
+    {
+        public ProviderViewModel(Provider provider, IEnumerable<ProviderUser> providerUsers)
+        {
+            Provider = provider;
+            UserCount = providerUsers.Count();
+
+            ProviderAdmins = string.Join(", ",
+                providerUsers
+                    .Where(u => u.Type == ProviderUserType.ProviderAdmin && u.Status == ProviderUserStatusType.Confirmed)
+                    .Select(u => u.Email));
+        }
+
+        public int UserCount { get; set; }
+
+        public Provider Provider { get; set; }
+        
+        public string ProviderAdmins { get; set; }
+    }
+}