Item scheduling/re-scheduling improvements

We have started work on improving behaviors and consequences of item schedule changes.

Mainly to cater for such use cases:

1. User wants to reschedule only single item without affecting it's dependencies.

2. User wants to reschedule only single item without affecting it's parent

3. User wants to reschedule single item but also dependencies should react and move accordingly. Lastly, make sure if previously there was a gap between item and it's successor dependencies - keep it or reduce based on user choice.

4. User wants to reschedule single item but also if it's a child item, update parent item schedule if child item affects it's total time range.