Support specifying the model location in the .mat files itself

[traversaro]

At the moment, the model corresponding to the dataset needs to be specified manually using the "Set Robot Model" menu. If that is not specified, the following error occurs:

[ERROR] ModelLoader :: loadModelFromFile : Error in parsing model from URDF.

It would be great if the model location could be encoded with a ROS or Gazebo style uri as part of dataset itself, so that the model could be directly opened if it is available, or a clear error printed if a given model is not available in the system/environment. Probably this would require also modifications on the blf's robot logger side.