switch adjustFeesForGas to use sdk.Coins #2411
Description
Summary
For the mempool fees, the adjustFeesForGas mechanism is currently dividing the amount of gas by the number of atoms per unit gas. Its more intuitive to change this to gasPrice, e.g. 1 gas = gasPrice coins. Its easiest to represent the gasPrice as sdk.Coins. We need to run through expected gas range of txs (perhaps 100 to 10 million), and expected reasonable price in atoms (perhaps .0001 atoms to 10 atoms?), and run through the logic just to ensure its all handled cleanly.