QtIFW

Fix missing redraw while pages are hidden but still existent.

Task-number: QTIFW-206

Fix issue when several pages are hidden, e.g. license and select
components page, caused by the fact that we've overwriten the wrong
virtual QWizard*::nextId() function.

We need to implement the logic inside the wizards page nextId()
function, as that one is called by the wizard anyway and by all
pages that call either QWizardPage::nextId() or QWizard::nextId().

Change-Id: I377c007be618431d708cb2712a86d61d0d4e104d
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>