Clean up and streamline config files to use with multiple suits, shoes, insoles

Currently, the two configuration files needed to run two xsens suits at the same time are available in [DEMO-laptop](https://github.com/robotology/wearables/tree/DEMO-laptop) branch of the upstream. The files are:

- https://github.com/robotology/wearables/blob/DEMO-laptop/app/xml/XsensSuitWearableDevice.xml
- https://github.com/robotology/wearables/blob/DEMO-laptop/app/xml/XsensSuitWearableDevice_second.xml

This is not a clean solution as we have to maintain these two files and update them separately in case of new parameters with future updates. Ideally, it is better to have a single xml configuration file, that takes a `prefix` parameter as input and launch the wearable device ports with that prefix. @traversaro is there anyway to pass a argument while launching `yarprobotinterface` with an xml configuration file.

CC @lrapetti @fjandrad @claudia-lat @diegoferigo @DanielePucci