Draft: improvements for gui_groups.py

* All actions are handled as transactions to make them undoable.
* In the Draft_AutoGroup menu groups are separated from layers.
* The Draft_NewLayer.svg icon is used for the New layer option.
* Selecting that option prompts for a layer name and also activates that layer.
* Icons and separators have been added to the Draft_AddToGroup menu.
* The task panel of that command has been replaced with a QInputDialog.getText dialog for consistency.

src/Mod/Draft/DraftGui.py

@@ -1421,10 +1421,15 @@ def setStyleButton(self):
         self.fontsize = fontsize
 
     def popupMenu(self,llist,ilist=None,pos=None):
-        """pops up a menu filled with the given list"""
+        """pops up a menu filled with the given list
+        
+        "---" in llist inserts a separator
+        """
         self.groupmenu = QtWidgets.QMenu()
         for i,l in enumerate(llist):
-            if ilist:
+            if "---" in l:
+                self.groupmenu.addSeparator()
+            elif ilist:
                 self.groupmenu.addAction(ilist[i],l)
             else:
                 self.groupmenu.addAction(l)