Core update. Base core features are done (main app doesn't compile)

Related Work Items: #416, #422, #423, #424

FoxTube.Core/Models/User.cs

@@ -13,6 +13,7 @@ using System.Threading.Tasks;
 using Windows.Storage;
 using YouTube;
 using YoutubeExplode;
+using FoxTube.Services;
 
 namespace FoxTube.Models
 {
@@ -36,10 +37,10 @@ namespace FoxTube.Models
 				catch (Exception e)
 				{
 					Metrics.SendReport(new Exception("Failed to unsubscribe", e));
-					return true; 
+					return true;
 				}
 
-				UserManagement.SubscriptionsChangedInvoker(this, subscription);
+				UserService.SubscriptionsChangedInvoker(this, subscription);
 				Subscriptions.Remove(subscription);
 
 				SaveSubscriptions();
@@ -77,7 +78,7 @@ namespace FoxTube.Models
 				};
 				Subscriptions.Add(subscription);
 
-				UserManagement.SubscriptionsChangedInvoker(this, subscription);
+				UserService.SubscriptionsChangedInvoker(this, subscription);
 
 				SaveSubscriptions();
 				return true;
@@ -86,7 +87,7 @@ namespace FoxTube.Models
 
 		private void SaveSubscriptions()
 		{
-			Dictionary<string, string> subs = Subscriptions.Select(i => 
+			Dictionary<string, string> subs = Subscriptions.Select(i =>
 				new KeyValuePair<string, string>(i.ChannelId, i.Avatar.Default__?.Url))
 				as Dictionary<string, string>;