Rework how CamelServices are added to CamelSession.
* Give CamelServices a simple unique ID string. That will be its identity from now on, not its URL. * Split adding a CamelService and retrieving a CamelService into two separate operations. Adding a CamelService requires both a UID and CamelURL (for now), retrieving a CamelService just requires the UID. * CamelService now implements the GInitable interface, replacing its construct() method.