GUI: possible issue with mapper after refactoring

In file ParameterTuningDelegate.cpp in function

QWidget* ParameterTuningDelegate::createEditor(QWidget* parent, const QStyleOptionViewItem& option,
                                               const QModelIndex& index) const

an old comment says about some problem:

// FIXME there is an issue with time of life of editor .vs. item

Probably it is about something occurred after removing mapper and SessionItem.

This should be cheked.

changed milestone to %20 GUI refactoring

added GUI label

mentioned in merge request !1263 (merged)

closed with merge request !1263 (merged)