Sorters should not always be removed on row drop

[bmblb]

Reported by client.

Steps to reproduce on advanced demo:

1. sort WBS column
2. swap two neighbot leaf tasks around
3. sorter is removed, but row stays in place

Sorter is removed because in general dropping the row would break sorting order. However, there are cases where that's not the case, which are:

1. we sort by WBS, which is calculated based on the position we are moving task to
2. we move task inside sorted subgroup (group of records with the same value on which sorter does not have affect)

Part of the problem is that cut/paste action does not remove the sorter, but essentially it is the same operation