Change List:
a) Refactored code: Shifted JSON message creation to
QmlV8DebuggerClientPrivate.
b) QScriptEngine is used for JSON instead of JsonValue and
JsonInputStream.
c) Locals Window displays all variables accessible in the current
context.

Change-Id: I82e73f6c57482408f5fc501c908aa96297d3d754
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>