PLCgen: Improve documenting PLC transition code steps
Currently the PLC code generator creates transition code without much comment. This means it may be difficult to follow what the code is computing.
To improve, the generator should create more comments in the transition code, with details what is being done (or not done), and why (if applicable).
#774 is close to this, but addresses the more general problem of names and easy to understand (magic) numbers. This issue is about comments in/for the code rather than the code itself.