Only emit the clicked() signal from views if the left button is used.

Only emit the clicked() signal from views if the left button is used.

This is consistent with QAbstractButton, QCalendarWidget,
QDialogButtonBox and QGroupBox (ie, all other widgets with
a clicked signal)

Task-number: QTBUG-26105

Change-Id: Ieafe988b5c03216796b69a7cd70ac1a03fc12b0a
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>