Improve structure of permutations to use unmodifiable capability lists

As discussed on the felix dev mailing list:

Implement a capability selection collection that
points to a constant list of capabilities and has an index to the currently
selected candidate for that permutation. That way there is no copying of
the constant list, instead we have a super lightweight collection that
points to the unmodifiable list of capabilities and just has an index.
Changing a Permutation would only involve incrementing that index instead
of removing from a copy on write list. We can then get rid of duplicate
capability lists since the list is unmodifiable it can be shared with
multiple selection index lists.