Added TizenControls singleton in Controls.Tizen plugin.

There should be no QtQUick.Controls.Styles.Tizen import in
applications. QtQuick.Controls.Tizen should be just enough.
Fixed examples

Change-Id: I298fc8b7b2a250392faf001d5ccde89c139ab180
Reviewed-by: Jarosław Staniek <staniek@kde.org>