Conform to the LC W3C Widget API specification

As the W3C Widgets API spec gets to last call (LC) status, we should ensure that Wookie is able to pass all conformance requirements. This means that we need to:

• update the self-test widget to conform to the spec; this widget includes test cases that helps us check conformance

• all metadata properties specified in the W3C Widget interface are available

• all metadata properties noted as READ-ONLY in the specification raise an appropriate exception if someone attempts to modify them

• methods are created to handle widget and height attribute requests appropriately

• the preferences object is instantiated correctly and behaves according to specification

• the openURL method is correctly implemented

• remove any attributes or methods left over from earlier drafts of the spec, e.g. showNotification, window modes etc

Overall, we need to ensure that all MUSTs in the spec are adhered to.

See also: http://dev.w3.org/2006/waf/widgets-api/