Fixed memory leak on QDeclarativeContactModel private data.

Changed QDeclarativeContactModel private data from pointer to QScopedPointer.

Change-Id: I07d0aa0f40cc4a592e0f44bde81c8dca8a797f9e
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Avoid create a new contact engine model if the current one is equal.

Check for engine name and manager-uri before recreate the contact engine.

Change-Id: I933cc9e6d67f39e69d76f46cc92a9b7b5853707f
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>