Implementing more "failure modes"

[karelbilek]

"Skip" mode is a bit nonsensical right now; if we "skip", we should also log skipped ones somewhere.

Example: the bitcoinjs/coinselect library sort results first by the percentage of skipped and only THEN by cost.

[karelbilek]

I am probably over-complicating the code in order to keep both current behaviour AND the behaviour I want :/