Fixed: Faster artist endpoint (#874)

* Fixed: Speed up AllArtist API endpoint

* New: Display UI before artists have loaded

* Add test of new repository methods

src/NzbDrone.Core/Datastore/BasicRepository.cs

@@ -58,7 +58,7 @@ namespace NzbDrone.Core.Datastore
 
         public IEnumerable<TModel> All()
         {
-            return DataMapper.Query<TModel>().ToList();
+            return Query.ToList();
         }
 
         public int Count()