Add exception conversion to ConverterService

[thboileau]

Initial ticket : http://restlet.tigris.org/issues/show_bug.cgi?id=878

[jlouvel]

I've added org.restlet.resource.@Status annotation type to automatically convert Throwable Java classes between HTTP statuses and error response entities.

Also added a unit test AnnotatedResource20TestCase as a starting point (fails). Next steps:

• community feed-back requested via mailing list, process if needed
• implementation the annotation processing, relying on ConverterService and StatusService.
• fix unit test and add more to verify client side and server side

Assigned to @thboileau for the implementation.

[jlouvel]

See discussion at http://restlet.tigris.org/ds/viewMessage.do?dsForumId=4447&dsMessageId=3079971