rtt_roscomm: Unified naming scheme for rtt_rosservice and use a singleton for the ROSServiceRegistryService

The first commit just renames a few files that had `ros_service` in their name so that all files and libraries have the `rtt_rosservice_` prefix. This is just a cleanup to avoid confusion with the `rtt_ros_service` located in package `rtt_ros`.

The second commit adds a singleton pattern to the `ROSServiceRegistryService` class and updated all classes that use that service to call the static `ROSServiceRegistryService::Instance()` method instead of relying that the service has already been loaded in the global service. This fixes an error if typekit packages that contain service proxies are imported without using the `ros.import()` operation. They will now load the `rosservice_registry` service automatically.