Remove QApplication::type() and make QCoreApplication::Type internal

Remove QApplication::type() and make QCoreApplication::Type internal

These Qt3 legacy application types do not match the application types
available in Qt5. Thus, the decision was to kill the confusing and
mostly useless type enum. Use for example qobject_cast instead to find
out the application type.

Task-number: QTBUG-28093
Change-Id: Ia8cf7c3ea98a3cea27f74760d62e519ea10bce9f
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>