Rank of Sub-tasks regardless to the Parent issue.

Currently in the task board, the ranking of the sub-tasks is restricted by the parent issue of those sub-tasks. However, in certain situations it's necessary to have this restriction removed. An example of the use case we have here:

Call ABC-1: parent call to create a piece of software
Call ABC-2, ABC-3, ABC-4, ABC-5 (sub-task from ABC-1): all three for the development of different parts of the software, one for customer documentation all assigned to different people

The people which the calls ABC-2, ABC-3, ABC-4, ABC-5 assigned see only the assigned calls on there agile boards. There is no chance for the users to get the ABC-2 calls above all other calls without re-ranking the complete call ABC-1 which is assigned to the product owner of the software.

It will be nice to have the flexibility for the users to have their issues ranked based on their own boards instead of having the restriction of the parent issue.