QmlV8DebuggerClient: Local Variables

Show "this" data in the locals window.
If handle is not present in ref list then fetch Local data
asynchronously. Insert the data when lookup request succeeds.

Change-Id: Ie342bcb963b76b8fcdb958979b59fb084fe50e51
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>