Use a list of <goal>s instead of a set

[nishantjr]

This has two advantages:

• It is more efficient, since when executing a strategy rules only try matching on the first goal, and not all the goals in the goal cell
• When functions use local-contexts we no longer need to specify a goalId

[h0nzZik]

What happens when user (using Kore) specifies multiple goals? How does the list of goals look when proving the second goal? Is the second goal on top of the list?

[nishantjr]

Since the k cell is merged with the the claim cell, $PGM is part of an initial goal.
Multiple claims are dispatched as subgoals one at a time with the first one being proved first.