Point and click to add an item to Design View

[ptsavol]

Add a new method to add items to Design View without drag-and-drop. Simply click on an item or specification in the Toolbar, then click on Design View to make a new item. I think this can co-exist with the drag-and-drop way of adding items, so old users are not confused.

Discussed in a UX meeting with @nelliputkonen, @jeenou, and @jkiviluo.

Should be implemented as part of #2785 or after.