[V8] Introduce a QML compilation mode

In QML mode, there is a second global object - known as the QML
global object.  During property resolution, if a property is not
present on the JS global object, it is resolved on the QML global
object.

This global object behavior is only enabled if a script is being
compiled in QML mode.  The object to use as the QML global object
is passed as a parameter to the Script::Run() method.  Any function
closures etc. created during the run will retain a reference to this
object, so different objects can be passed in different script
runs.

Change-Id: Ib6b4ed363b7e8089d38a9cdcfb0d3b314dc333ca
Reviewed-by: Simon Hausmann <simon.hausmann@nokia.com>