automatically adjust contract pricing
Created by: ChrisSchinnerl
This PR is pretty much the successor of PR#2070. It's easier and simply uses the transactionpool to figure out the correct fees for the contract price. It also changes a few parts in the code that previously used the internal settings to use the external ones. I think the internal settings are meant to provide a minimum while the external ones reflect the current price of the renter. Therefore we should probably use the external ones if we do stuff like checking if the renter pays enough for bandwidth.