Revert "velocity servos use joint parameter directly (works also for slider)"
This reverts commit ecdeae47c38f4f998dcca42cdbc64367980740c8.
And also implements a SliderServoVel

Conflicts:
	ode_robots/robots/uwo.cpp
	ode_robots/robots/uwo.h
	ode_robots/simulations/uwo/main.cpp