Renumbering of selected items in deselection of an item

If an item is deselected and there are items with higher index numbers now this elements are renumbered to follow the sequence

Signed-off-by: Arturo <Arturo@MacBook-Pro-de-Arturo.local>
Merge pull request #96 from ArturoMarzo/master

Renumbering of selected items in deselection of an item