Allows completion of local variable and function names.

Task-number: QTCREATORBUG-942
Reviewed-by: Roberto Raggi

* The "Script" type is now implicitly available without imports.
* No errors for bindings inside a Connections element.

Reviewed-by: Roberto Raggi

By always setting the scope object, even if it is identical to the root
object.

Done-with: Erik Verbruggen