SplitView: Disconnect items connections on destruction
SplitView: Disconnect items connections on destruction

Those connections are sometimes called after the SplitView has
been destructed and it causes warnings (i.e. tst_splitview autotests).

Change-Id: I42ae333e72c01edba78f69bb1e9de8b4f85dea2c
Reviewed-by: Richard Moe Gustavsen <881e230b58d8abf8efbd9b8ce5a2db05f1d53614@digia.com>

mizukusak/qtquickcontrols,mizukusak/qtquickcontrols,drgvond/qtquickcontrols,jfaust/qtquickcontrols,richardmg/qtcomponents,richardmg/qtcomponents,jfaust/qtquickcontrols,drgvond/qtquickcontrols,mizukusak/qtquickcontrols,drgvond/qtquickcontrols,jfaust/qtquickcontrols,kobolabs/qtquickcontrols,richardmg/qtcomponents,kobolabs/qtquickcontrols,kobolabs/qtquickcontrols