group and subgroup adding/editing, services added

TimetableDesigner.Core/Subgroup.cs

@@ -6,12 +6,22 @@ using System.Threading.Tasks;
 
 namespace TimetableDesigner.Core
 {
-    public class Subgroup
+    public class Subgroup : IGroup
     {
         #region PROPERTIES
 
         public string Name { get; set; }
-        public string Description { get; set; }
+
+        #endregion
+
+
+
+        #region CONSTRUCTORS
+
+        public Subgroup()
+        {
+            Name = string.Empty;
+        }
 
         #endregion
     }