Fix crash when deleting component in Component.onComplete through loader

This is a regression introduced with Qt 5.3.0. The recursion watcher code that
is supposed to handle the test case of QTBUG-39775 can detect the recursion
into the object creator. However the boolean that indicates the recursion is a
member of a structure that's deleted afterwards. To avoid access to deleted
memory, this patch simply reference counts data structure shared between the
creators and also wraps the recursion watcher into a convenience class that
also increases/decreases the reference count accordingly.

Change-Id: I8d2e3e200ab1295e89d951e09f187d382a056d5a
Task-number: QTBUG-39775
Reviewed-by: Lars Knoll <lars.knoll@digia.com>