Add project files.

OemanTrader.Domain/Services/IDataService.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace OemanTrader.Domain.Services
+{
+    public interface IDataService<T>
+    {
+        Task<IEnumerable<T>> GetAll();
+        Task<T> Get(int id);
+        Task<T> Create(T entity);
+        Task<T> Update(int Id, T entity);
+        Task<bool> Delete(int Id);
+    }
+}