Debugger: Populate "Source Files" for QML, showing shadow .js structure

Request the sources actually seen by v8, and show them in a separate file
(click on the leftmost column). Automatically populating 'Source Files'
and also making the functionality available for mixed debugging requires
some more thought ...

Change-Id: Id8f55eed9c842b545434a6c608fb34d370a8f8bb
Reviewed-by: Aurindam Jana <aurindam.jana@nokia.com>