Customize installation page: update title and subtitle

Component selection page subtitle is not changed yet, it is a bit trickier as the IFW itself changes the text right before entering the page as the text varies depending on what you have selected on previous page. Current subtitle is one of these : static const char *strings[] = { QT_TR_NOOP("Please select the components you want to update."), QT_TR_NOOP("Please select the components you want to install."), QT_TR_NOOP("Please select the components you want to uninstall."), QT_TR_NOOP("Select the components to install. Deselect installed components to uninstall them.<br>Any components already installed will not be updated."), QT_TR_NOOP("Mandatory components need to be updated first before you can select other components to update.") } ;