Change placeholder python code (OpMode, etc) to match Peter's API

[lizlooney]

Peter's PR: wpilibsuite/allwpilib#7744

Look at the C++ code in
wpilibc/src/main/native/cpp/opmode/PeriodicOpMode.cpp
and the python wrappers in:
wpilibc/src/main/python/semiwrap

[lizlooney]

wpilibjExamples/src/main/java/org/wpilib/templates/romieducational/EducationalRobot.java shows how to add/publish opmodes.