Improve the flow of adding an item to a menu

As part of page management implementation CMS7-7709 and HSTTWO-2836, it should be possible to create a menu item using Angular modal dialog which is possible. But it is not possible to create a menu item at root level. Because by default a menu item is always selected, so when user attempts to create a menu item it is always nested. Workaround is possible but inconvenient: after creation user has to drag it out to root level manually.

To improve the flow, two improvements should be implemented:

• Fix that when adding a new menu item, the newly added menu item is visible in the tree
• A new logic "where" a newly added item is placed in the tree should be implemented. This logic is described in the attached document.