Severa changes:

    - fix XSS vulnerability caused by leading space
    - fix nested popup widget cancelling as well as not correctly calling render() of stubbed WCompositeWidget (#3242)
    - make WStandardItemModel robust against header data requests outside geometry (#2408)
    - added missing icon files (#2312)
    - fixed setting text later on checkbox (#2293)
    - fix tooltip not showing when wrapped inside a button (#2256)
    - allow non-modal dialog to raise to front using titlebar click (#2167)
    - document limitation of WDialog::exec() + non-event thread (#976)