Bug 21946: Update Administration->Item types to allow for defining parent types

Bug 21946: Update Administration->Item types to allow for defining parent types

To test:
1 - Browse to Administration -> Item types
2 - Not a new colum for prent type
3 - Edit an existing type and not you can select any type (except the current) as a parent
4 - Select one
5 - Edit the type you selected as parent
6 - Note it cannot have a parent defined
7 - Edit a new type, note you can select a parent

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Lisette Scheer <lisetteslatah@gmail.com>
Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>