Ensure correct abstraction of training class

[mauicv]

currently we have and Env class and then a StandingEnv and WalkingEnv class that derive from it. I think this is correct, but should be reviewed. The behavour we want is that given some behavour we want the quadruped to learn it should implemented as a EnvBehavour class. It might be possible to ensure this is the only code that needs to be touched and the training functionality is common across all training tasks.