Now we use a specific notation (⊑) to whose arguments we interpret
in uPred_scope. This makes notations much more concise.

Also introduce a notion for valid to be timeless.

* Remove the order from RAs, it is now defined in terms of the ⋅ operation.
* Define ownership using the step-indexed order.
* Remove the order also from DRAs and change STS accordingly. While doing
  that, I changed STS to no longer use decidable token sets, which removes the
  requirement of decidable equality on tokens.