JSBridge-Core-ct.11: Fix superclass of JSException

[LinqLover]

One should (always) never subclass from Exception itself, but most of the time from Error or Notification or one of its subclasses. Exception is an abstract class, and the previous implementation led to SubclassResponsibility errors from Exception>>defaultAction when signaling a JSException. Since JavaScript errors do not have Smalltalk''s coroutine capabilities, subclassing from Error seems a perfect match in this case.