Port the examples models in tutorial/model to avoid use implicit wrappers

[traversaro]

As the desired for the future is to avoid to continue to use the implicit wrappers created by the plugins, but rather just let the plugins create the YARP devices encapsulating Gazebo functionalities and sensors, and always allocate wrappers via the gazebo_yarp_robotinterface plugin, we should also port the example models in https://github.com/robotology/gazebo-yarp-plugins/tree/master/tutorial/model to use the gazebo_yarp_robotinteface rather then relying on implicit wrappers.

cc @drdanz @ste93 @randaz81

[traversaro]

fyi @Nicogene @GrmanRodriguez

[traversaro]

Example migration: https://github.com/robotology/cer-sim/commits/devel/gazebo/cer .

[traversaro]

I started with the first model (camera) but I discovered that gazebo_yarp_camera still needs to be migrated to support the use of gazebo_yarp_robotinterface plugin, see #612 .