OnOffControl access to commanded setpoint.

[ldwoolley]

The training description shows the setpoint command signal, but that signal is not available because it was declared under "protected" in the Implementation module for OnOffControl, OnOffControl_WithHisteresis, ConventionalPIControl, and ConventionalOnOffControl. The models all work, and match the data presented in: https://mbe.modelica.university/components/architectures/thermal_control/. However, the data presented compares the actual temperature to the sensor temperature and to the commanded setpoint. You can not plot the setpoint with the current implementation that has the Trapezoid setpoint_signal under a protected declaration. I pulled these out on my copy of the code and was able to access the commands without issue. I ask the question for the creaters, do they intentionally want to hid the setpoint signal behind the protected declaration so the reader has to figure out where the signal went, or do they want the plots to be readily available when the example models are run?

If they want to make a change, I am happy to adjust the code and submit a pull request. Looking for your guidance.