group and subgroup adding/editing, services added

TimetableDesigner.Core/IGroup.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace TimetableDesigner.Core
+{
+    public interface IGroup
+    {
+        #region PROPERTIES
+
+        string Name { get; }
+
+        #endregion
+    }
+}