QKeySequenceEdit: make setKeySequence a slot

There's a signal keySequenceChanged(QKeySequence), so the setter
should be a slot, too.

Change-Id: I6591bad071444ffa252a2fdb9ccaf28e8629f59c
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
QKeySequenceEdit: give nested line edit an objectName

People request this, and other widgets do this, too (say, QSpinBox).

Change-Id: I275537fb82b805b0dcb8edba87b8e234985f8d1f
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Remove a boolean trap in QLayout::replaceWidget

Use some flags instead.

Task-number: QTBUG-34668
Change-Id: I9a75253c8eb98164c594bb6bb06c1a16c9609537
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>