Fix QmldirCache object leak

Delete all the QmldirCache objects in the linked list

Change-Id: I9948ccce3d72aaed4f8b14b131e040177d7a15ef
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>
Fix QQmlContextData object leak

Mark the QQmlContextData object created in QmlContextWrapper::urlScope()
as owned by its QmlContextWrapper to prevent leak.

Change-Id: Ie7afee676e0745a78ef4f3a56984f52f638227e0
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>