Removed some dead code on the interfaces. Introduced UnitOfWork to simplify repo injection.

API/Interfaces/IUnitOfWork.cs

@@ -0,0 +1,13 @@
+using System.Threading.Tasks;
+
+namespace API.Interfaces
+{
+    public interface IUnitOfWork
+    {
+        ISeriesRepository SeriesRepository { get; }
+        IUserRepository UserRepository { get; }
+        ILibraryRepository LibraryRepository { get; }
+        Task<bool> Complete();
+        bool HasChanges();
+    }
+}