FeePoolEternalStorage is currently used only to store the last fee withdrawal timestamp for each address. See
FeePool.feesByPeriod for details of what this information is used for.
This contract is just wrapper around EternalStorage with a limited setup period and a setup function that sets each account's last fee withdrawal times.
constructor(address _owner, address _feePool)
This is a helper to import fee withdrawal information from a previous version of the system during the setup period.