Lots of changes to get code ready to add library.

API/Interfaces/ILibraryRepository.cs

@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using API.DTOs;
+using API.Entities;
+
+namespace API.Interfaces
+{
+    public interface ILibraryRepository
+    {
+        void Update(Library library);
+        Task<bool> SaveAllAsync();
+        Task<IEnumerable<LibraryDto>> GetLibrariesAsync();
+        /// <summary>
+        /// Checks to see if a library of the same name exists. We only allow unique library names, no duplicates per LibraryType.
+        /// </summary>
+        /// <param name="libraryName"></param>
+        /// <returns></returns>
+        Task<bool> LibraryExists(string libraryName);
+    }
+}