[WIP] [FN] Fee estimator
Reopening this as a new PR with the latest master branch merged in.
Original work by AndrewZvvv in #1486
Still needs to be reviewed in its entirety, particularly the estimation algorithm portion. The merge may also not have been entirely clean due to the length of time involved.
My initial understanding of this is that the Algorithm014 folder represents the implementation as it existed in Bitcoin Core 0.14. There were changes in 0.15 described here:
https://gist.github.com/morcos/d3637f015bc4e607e1fd10d8351e9f41
So I think review effort should concentrate on the TxConfirmStats and BlockPolicyEstimator that are not in the Algorithm014 folder. I think at some point the extra files can be deleted entirely, but I want to be sure we don't need them for anything first.