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.
Right now the only difference between the two createInputs seem to be that this one expects a blockHeight/blockTxIndex, but its name doesn't convey that. I think this one should be called createInputsOnBlock() or something like that