Restrict level change

[abernh]

allows to restrict movement within depths, e.g. keeping items restricted to their original depth all along while still allowing complete sorting of all levels.

[SimonOrdo]

@abernh Assuming allow is false for both... it doesn't seem to allow dropping on to a different parent if that parent does not already have children. Any idea how to fix that? Thanks for the update!

[chewmunyoke]

@SimonOrdo I have made additional changes in my PR to fix your problem. Hope you find it helpful :)