Use new connect() signal/slot syntax
- Remove some Q_PRIVATE_SLOT usage, and the k prefix from method names, not needed any more.
- With QPushButton, always use '&QPushButton::clicked'... etc rather than '&QAbstractButton::clicked' in connect() calls, the rationale is QAbstractButton is just the base/abstract class used by upstream (from dfaure); generally the same rationale applies to other sub-classes of QAbstractButton NO_CHANGELOG