Fee Estimation #145
Description
Fee Estimation ported from bitcoin core
Copy over the code for fee estimation from stratis repo
This PR was initially started by @AndrewZvvv
stratisproject/StratisBitcoinFullNode#1486
And continues here and later by @zeptin
stratisproject/StratisBitcoinFullNode#4040
Due to the link between repos now removed the code probably needs to be copied over