Improve performance of the QML front-end

Improve performance of the QML front-end

Introduced a new lexer and a more efficient representation of
the AST. Instead of creating unique name ids, we simply use
QStringRef(s).

Change-Id: I403472fa2bb74d2c87dd6314065306499677a3bf
Authored-by: Roberto Raggi
Reviewed-on: http://codereview.qt.nokia.com/3750
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>