Replace QV8QObjectResource with QV4::QObjectWrapper

Use a proper sub-class instead of external object resources, as a first
step towards porting the QObject bindings away from V8.

This also replaces the function template / constructor approach and the
faster getter optimization with a plain virtual get in the V4::Object.

Property lookup in QObject bindings will be subject to future optimizations
that will work very differently once we enable the faster V4 lookup mechanism
in QML.

Change-Id: Ib7c2eead5323c22290c2924de786d9cfcf308c03
Reviewed-by: Lars Knoll <lars.knoll@digia.com>