重构项目结构，移除Assignment相关功能，优化Submission模块

Entities/DTO/Common/QueryParameterDto.cs

@@ -0,0 +1,15 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Entities.DTO
+{
+	public class QueryParameterDto
+	{
+		public int PageIndex { get; set; }
+		public int PageSize { get; set; }
+		public string Search { get; set; }
+	}
+}