Implemented IVelocityControl2

I implemented IVelocityControl2.
Can @traversaro or @jeljaik   check this on the workstation before merging into `development`?

Once this is done we can change the `if` condition in https://github.com/robotology-playground/yarp-wholebodyinterface/commit/3bfcac8e72675bcc20b5eaba475247fb18bdedbb to be `isiCubSimulator`.