Descriptions for new command framework

[GoateSo]

Doesn't explain in depth the command based framework as laid out here.

Possible idea could be to introduce general project organization -> command classes (old) -> command factories and combinators as an alternative, then going into the things which can be done with it

• slim down doc 5 - program organization to focus on general organization and subsystems
• include section discussing lambdas and functional interfaces (either in doc 3, or in a new doc)
• add new doc 6 - commands to talk about the approaches (command classes (old) -> factories and combinators as alternative)

[GoateSo]

• update documentation to reflect upcoming deprecation of SubsystemBase and CommandBase:

Moves all CommandBase functionality into Command and deprecates CommandBase for removal.
Moves all SubsystemBase functionality into Subsystem and deprecates SubsystemBase for removal.
Adds a function to CommandScheduler to remove all registered Subsystems.