Convert diagonal clock constraints in simulation when possible

[seblund]

Here is how clock constraints are shown in the simulation tool now (SW5): We can and should convert expression with cycles like this to x=y=z, to avoid as many diagonal constraints (x-y<=c) as possible because they are generally confusing.

We should also convert 0-x<=c to -c<=x (if that is not already done)

[Nielswps]

This has been implemented on the simulator branch but does not account for circular connections