Ability to sum sub-tasks remaining effort at parent issue level

The idea is to have the parent issue remaining effort composed of the sum of the remaining of its children.
In order to support gross estimates approach versus refined over the release cycle, the following rule should be applied as well: change the remaining of the parent issue only when the sum of the remaining for the children is higher to the current remaining at parent level.

Without this feature, it's a pain for people (mostly PM) to efficiently track the remaining effort on a given release, or to identifed which remaining effort is the most relevant.