Services configuration format choice for bundle generation with the 'annotation' format

When you chose 'annotation' as the generated configuration files format, 'xml' is used for the services configuration file and there is no way to chose another format.

With this patch, when 'annotation' is chosen, the user will be asked to chose a format for the services configuration.

I'm not quite sure about the etiquette with pull-requests here (maybe I should open an issue first ?), and this patch might not be really elegant, but here is my proposition anyway :-)