Input selection algorithm

Rebased to vp-withdrawal.

Note I had to make some minor changes to make the test run again.

Also the createInputs and createInputsStore needs to be cleaned up. They are both taking a store right now and especially the createInputsStore name is misleading.
And I like your thoughts. I have been working and thinking too long in a purely functional way. It totally makes sense. So I get it now - it could be thought of as if we are asking if the votingpool itself is eligible.

Renaming to isCreditEligible.