fix #450 Number controller didn't reference the right configuration error message.

aria.widgets.Widget.INVALID_CONFIGURATION has been moved to aria.core.JsonValidator.INVALID_CONFIGURATION,
after commit b129e79
fix #451 Change test url in jsonp test

We used to target twitter for testing real jsonp requests. Lately twitter API became rate limited and thus failing from time to time.
This changes to jsfiddle echo service.