Checking FeeUTXO Amount about plasma-mvp-sidechain

[colin-axner]

Upon further discussion, instead of including a feeutxo within a block we have decided instead to include the feeAmount into the state hash. By ensuring that the feeAmount is included into the state hash (perhaps in endblocker) we can use the state hash to verify how much in fees should be allowed to be withdrawn through the root contract.

We need to determine how we can ensure the fee amount for each block is included into the state hash and how we can get a merkle proof to show that it has been included.

[AdityaSripal]

This issue should be changed to the larger issue of how to handle fees in general.