Add reserves info to fee method

[mDuo13]

The fee method provides info about transaction costs/fees but doesn't tell you about the cost of reserves, which is similarly useful information often used together. In particular, the transaction cost for an AccountDelete (and, in XLS-30d, AMMCreate) is one owner reserve increment, so it would be useful to know this info for setting the Fee of those transactions.

One can get this from server_info/server_state now, but those methods are more work for the server than fee.